Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/lrg/voltage-2.6
[linux-2.6.git] / fs / buffer.c
1 /*
2  *  linux/fs/buffer.c
3  *
4  *  Copyright (C) 1991, 1992, 2002  Linus Torvalds
5  */
6
7 /*
8  * Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
9  *
10  * Removed a lot of unnecessary code and simplified things now that
11  * the buffer cache isn't our primary cache - Andrew Tridgell 12/96
12  *
13  * Speed up hash, lru, and free list operations.  Use gfp() for allocating
14  * hash table, use SLAB cache for buffer heads. SMP threading.  -DaveM
15  *
16  * Added 32k buffer block sizes - these are required older ARM systems. - RMK
17  *
18  * async buffer flushing, 1999 Andrea Arcangeli <andrea@suse.de>
19  */
20
21 #include <linux/kernel.h>
22 #include <linux/syscalls.h>
23 #include <linux/fs.h>
24 #include <linux/mm.h>
25 #include <linux/percpu.h>
26 #include <linux/slab.h>
27 #include <linux/capability.h>
28 #include <linux/blkdev.h>
29 #include <linux/file.h>
30 #include <linux/quotaops.h>
31 #include <linux/highmem.h>
32 #include <linux/module.h>
33 #include <linux/writeback.h>
34 #include <linux/hash.h>
35 #include <linux/suspend.h>
36 #include <linux/buffer_head.h>
37 #include <linux/task_io_accounting_ops.h>
38 #include <linux/bio.h>
39 #include <linux/notifier.h>
40 #include <linux/cpu.h>
41 #include <linux/bitops.h>
42 #include <linux/mpage.h>
43 #include <linux/bit_spinlock.h>
44
45 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
46
47 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
48
49 inline void
50 init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
51 {
52         bh->b_end_io = handler;
53         bh->b_private = private;
54 }
55
56 static int sync_buffer(void *word)
57 {
58         struct block_device *bd;
59         struct buffer_head *bh
60                 = container_of(word, struct buffer_head, b_state);
61
62         smp_mb();
63         bd = bh->b_bdev;
64         if (bd)
65                 blk_run_address_space(bd->bd_inode->i_mapping);
66         io_schedule();
67         return 0;
68 }
69
70 void __lock_buffer(struct buffer_head *bh)
71 {
72         wait_on_bit_lock(&bh->b_state, BH_Lock, sync_buffer,
73                                                         TASK_UNINTERRUPTIBLE);
74 }
75 EXPORT_SYMBOL(__lock_buffer);
76
77 void unlock_buffer(struct buffer_head *bh)
78 {
79         clear_bit_unlock(BH_Lock, &bh->b_state);
80         smp_mb__after_clear_bit();
81         wake_up_bit(&bh->b_state, BH_Lock);
82 }
83
84 /*
85  * Block until a buffer comes unlocked.  This doesn't stop it
86  * from becoming locked again - you have to lock it yourself
87  * if you want to preserve its state.
88  */
89 void __wait_on_buffer(struct buffer_head * bh)
90 {
91         wait_on_bit(&bh->b_state, BH_Lock, sync_buffer, TASK_UNINTERRUPTIBLE);
92 }
93
94 static void
95 __clear_page_buffers(struct page *page)
96 {
97         ClearPagePrivate(page);
98         set_page_private(page, 0);
99         page_cache_release(page);
100 }
101
102
103 static int quiet_error(struct buffer_head *bh)
104 {
105         if (!test_bit(BH_Quiet, &bh->b_state) && printk_ratelimit())
106                 return 0;
107         return 1;
108 }
109
110
111 static void buffer_io_error(struct buffer_head *bh)
112 {
113         char b[BDEVNAME_SIZE];
114         printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
115                         bdevname(bh->b_bdev, b),
116                         (unsigned long long)bh->b_blocknr);
117 }
118
119 /*
120  * End-of-IO handler helper function which does not touch the bh after
121  * unlocking it.
122  * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
123  * a race there is benign: unlock_buffer() only use the bh's address for
124  * hashing after unlocking the buffer, so it doesn't actually touch the bh
125  * itself.
126  */
127 static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
128 {
129         if (uptodate) {
130                 set_buffer_uptodate(bh);
131         } else {
132                 /* This happens, due to failed READA attempts. */
133                 clear_buffer_uptodate(bh);
134         }
135         unlock_buffer(bh);
136 }
137
138 /*
139  * Default synchronous end-of-IO handler..  Just mark it up-to-date and
140  * unlock the buffer. This is what ll_rw_block uses too.
141  */
142 void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
143 {
144         __end_buffer_read_notouch(bh, uptodate);
145         put_bh(bh);
146 }
147
148 void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
149 {
150         char b[BDEVNAME_SIZE];
151
152         if (uptodate) {
153                 set_buffer_uptodate(bh);
154         } else {
155                 if (!buffer_eopnotsupp(bh) && !quiet_error(bh)) {
156                         buffer_io_error(bh);
157                         printk(KERN_WARNING "lost page write due to "
158                                         "I/O error on %s\n",
159                                        bdevname(bh->b_bdev, b));
160                 }
161                 set_buffer_write_io_error(bh);
162                 clear_buffer_uptodate(bh);
163         }
164         unlock_buffer(bh);
165         put_bh(bh);
166 }
167
168 /*
169  * Various filesystems appear to want __find_get_block to be non-blocking.
170  * But it's the page lock which protects the buffers.  To get around this,
171  * we get exclusion from try_to_free_buffers with the blockdev mapping's
172  * private_lock.
173  *
174  * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
175  * may be quite high.  This code could TryLock the page, and if that
176  * succeeds, there is no need to take private_lock. (But if
177  * private_lock is contended then so is mapping->tree_lock).
178  */
179 static struct buffer_head *
180 __find_get_block_slow(struct block_device *bdev, sector_t block)
181 {
182         struct inode *bd_inode = bdev->bd_inode;
183         struct address_space *bd_mapping = bd_inode->i_mapping;
184         struct buffer_head *ret = NULL;
185         pgoff_t index;
186         struct buffer_head *bh;
187         struct buffer_head *head;
188         struct page *page;
189         int all_mapped = 1;
190
191         index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
192         page = find_get_page(bd_mapping, index);
193         if (!page)
194                 goto out;
195
196         spin_lock(&bd_mapping->private_lock);
197         if (!page_has_buffers(page))
198                 goto out_unlock;
199         head = page_buffers(page);
200         bh = head;
201         do {
202                 if (!buffer_mapped(bh))
203                         all_mapped = 0;
204                 else if (bh->b_blocknr == block) {
205                         ret = bh;
206                         get_bh(bh);
207                         goto out_unlock;
208                 }
209                 bh = bh->b_this_page;
210         } while (bh != head);
211
212         /* we might be here because some of the buffers on this page are
213          * not mapped.  This is due to various races between
214          * file io on the block device and getblk.  It gets dealt with
215          * elsewhere, don't buffer_error if we had some unmapped buffers
216          */
217         if (all_mapped) {
218                 printk("__find_get_block_slow() failed. "
219                         "block=%llu, b_blocknr=%llu\n",
220                         (unsigned long long)block,
221                         (unsigned long long)bh->b_blocknr);
222                 printk("b_state=0x%08lx, b_size=%zu\n",
223                         bh->b_state, bh->b_size);
224                 printk("device blocksize: %d\n", 1 << bd_inode->i_blkbits);
225         }
226 out_unlock:
227         spin_unlock(&bd_mapping->private_lock);
228         page_cache_release(page);
229 out:
230         return ret;
231 }
232
233 /* If invalidate_buffers() will trash dirty buffers, it means some kind
234    of fs corruption is going on. Trashing dirty data always imply losing
235    information that was supposed to be just stored on the physical layer
236    by the user.
237
238    Thus invalidate_buffers in general usage is not allwowed to trash
239    dirty buffers. For example ioctl(FLSBLKBUF) expects dirty data to
240    be preserved.  These buffers are simply skipped.
241   
242    We also skip buffers which are still in use.  For example this can
243    happen if a userspace program is reading the block device.
244
245    NOTE: In the case where the user removed a removable-media-disk even if
246    there's still dirty data not synced on disk (due a bug in the device driver
247    or due an error of the user), by not destroying the dirty buffers we could
248    generate corruption also on the next media inserted, thus a parameter is
249    necessary to handle this case in the most safe way possible (trying
250    to not corrupt also the new disk inserted with the data belonging to
251    the old now corrupted disk). Also for the ramdisk the natural thing
252    to do in order to release the ramdisk memory is to destroy dirty buffers.
253
254    These are two special cases. Normal usage imply the device driver
255    to issue a sync on the device (without waiting I/O completion) and
256    then an invalidate_buffers call that doesn't trash dirty buffers.
257
258    For handling cache coherency with the blkdev pagecache the 'update' case
259    is been introduced. It is needed to re-read from disk any pinned
260    buffer. NOTE: re-reading from disk is destructive so we can do it only
261    when we assume nobody is changing the buffercache under our I/O and when
262    we think the disk contains more recent information than the buffercache.
263    The update == 1 pass marks the buffers we need to update, the update == 2
264    pass does the actual I/O. */
265 void invalidate_bdev(struct block_device *bdev)
266 {
267         struct address_space *mapping = bdev->bd_inode->i_mapping;
268
269         if (mapping->nrpages == 0)
270                 return;
271
272         invalidate_bh_lrus();
273         invalidate_mapping_pages(mapping, 0, -1);
274 }
275
276 /*
277  * Kick pdflush then try to free up some ZONE_NORMAL memory.
278  */
279 static void free_more_memory(void)
280 {
281         struct zone *zone;
282         int nid;
283
284         wakeup_pdflush(1024);
285         yield();
286
287         for_each_online_node(nid) {
288                 (void)first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
289                                                 gfp_zone(GFP_NOFS), NULL,
290                                                 &zone);
291                 if (zone)
292                         try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
293                                                 GFP_NOFS, NULL);
294         }
295 }
296
297 /*
298  * I/O completion handler for block_read_full_page() - pages
299  * which come unlocked at the end of I/O.
300  */
301 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
302 {
303         unsigned long flags;
304         struct buffer_head *first;
305         struct buffer_head *tmp;
306         struct page *page;
307         int page_uptodate = 1;
308
309         BUG_ON(!buffer_async_read(bh));
310
311         page = bh->b_page;
312         if (uptodate) {
313                 set_buffer_uptodate(bh);
314         } else {
315                 clear_buffer_uptodate(bh);
316                 if (!quiet_error(bh))
317                         buffer_io_error(bh);
318                 SetPageError(page);
319         }
320
321         /*
322          * Be _very_ careful from here on. Bad things can happen if
323          * two buffer heads end IO at almost the same time and both
324          * decide that the page is now completely done.
325          */
326         first = page_buffers(page);
327         local_irq_save(flags);
328         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
329         clear_buffer_async_read(bh);
330         unlock_buffer(bh);
331         tmp = bh;
332         do {
333                 if (!buffer_uptodate(tmp))
334                         page_uptodate = 0;
335                 if (buffer_async_read(tmp)) {
336                         BUG_ON(!buffer_locked(tmp));
337                         goto still_busy;
338                 }
339                 tmp = tmp->b_this_page;
340         } while (tmp != bh);
341         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
342         local_irq_restore(flags);
343
344         /*
345          * If none of the buffers had errors and they are all
346          * uptodate then we can set the page uptodate.
347          */
348         if (page_uptodate && !PageError(page))
349                 SetPageUptodate(page);
350         unlock_page(page);
351         return;
352
353 still_busy:
354         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
355         local_irq_restore(flags);
356         return;
357 }
358
359 /*
360  * Completion handler for block_write_full_page() - pages which are unlocked
361  * during I/O, and which have PageWriteback cleared upon I/O completion.
362  */
363 static void end_buffer_async_write(struct buffer_head *bh, int uptodate)
364 {
365         char b[BDEVNAME_SIZE];
366         unsigned long flags;
367         struct buffer_head *first;
368         struct buffer_head *tmp;
369         struct page *page;
370
371         BUG_ON(!buffer_async_write(bh));
372
373         page = bh->b_page;
374         if (uptodate) {
375                 set_buffer_uptodate(bh);
376         } else {
377                 if (!quiet_error(bh)) {
378                         buffer_io_error(bh);
379                         printk(KERN_WARNING "lost page write due to "
380                                         "I/O error on %s\n",
381                                bdevname(bh->b_bdev, b));
382                 }
383                 set_bit(AS_EIO, &page->mapping->flags);
384                 set_buffer_write_io_error(bh);
385                 clear_buffer_uptodate(bh);
386                 SetPageError(page);
387         }
388
389         first = page_buffers(page);
390         local_irq_save(flags);
391         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
392
393         clear_buffer_async_write(bh);
394         unlock_buffer(bh);
395         tmp = bh->b_this_page;
396         while (tmp != bh) {
397                 if (buffer_async_write(tmp)) {
398                         BUG_ON(!buffer_locked(tmp));
399                         goto still_busy;
400                 }
401                 tmp = tmp->b_this_page;
402         }
403         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
404         local_irq_restore(flags);
405         end_page_writeback(page);
406         return;
407
408 still_busy:
409         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
410         local_irq_restore(flags);
411         return;
412 }
413
414 /*
415  * If a page's buffers are under async readin (end_buffer_async_read
416  * completion) then there is a possibility that another thread of
417  * control could lock one of the buffers after it has completed
418  * but while some of the other buffers have not completed.  This
419  * locked buffer would confuse end_buffer_async_read() into not unlocking
420  * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
421  * that this buffer is not under async I/O.
422  *
423  * The page comes unlocked when it has no locked buffer_async buffers
424  * left.
425  *
426  * PageLocked prevents anyone starting new async I/O reads any of
427  * the buffers.
428  *
429  * PageWriteback is used to prevent simultaneous writeout of the same
430  * page.
431  *
432  * PageLocked prevents anyone from starting writeback of a page which is
433  * under read I/O (PageWriteback is only ever set against a locked page).
434  */
435 static void mark_buffer_async_read(struct buffer_head *bh)
436 {
437         bh->b_end_io = end_buffer_async_read;
438         set_buffer_async_read(bh);
439 }
440
441 void mark_buffer_async_write(struct buffer_head *bh)
442 {
443         bh->b_end_io = end_buffer_async_write;
444         set_buffer_async_write(bh);
445 }
446 EXPORT_SYMBOL(mark_buffer_async_write);
447
448
449 /*
450  * fs/buffer.c contains helper functions for buffer-backed address space's
451  * fsync functions.  A common requirement for buffer-based filesystems is
452  * that certain data from the backing blockdev needs to be written out for
453  * a successful fsync().  For example, ext2 indirect blocks need to be
454  * written back and waited upon before fsync() returns.
455  *
456  * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
457  * inode_has_buffers() and invalidate_inode_buffers() are provided for the
458  * management of a list of dependent buffers at ->i_mapping->private_list.
459  *
460  * Locking is a little subtle: try_to_free_buffers() will remove buffers
461  * from their controlling inode's queue when they are being freed.  But
462  * try_to_free_buffers() will be operating against the *blockdev* mapping
463  * at the time, not against the S_ISREG file which depends on those buffers.
464  * So the locking for private_list is via the private_lock in the address_space
465  * which backs the buffers.  Which is different from the address_space 
466  * against which the buffers are listed.  So for a particular address_space,
467  * mapping->private_lock does *not* protect mapping->private_list!  In fact,
468  * mapping->private_list will always be protected by the backing blockdev's
469  * ->private_lock.
470  *
471  * Which introduces a requirement: all buffers on an address_space's
472  * ->private_list must be from the same address_space: the blockdev's.
473  *
474  * address_spaces which do not place buffers at ->private_list via these
475  * utility functions are free to use private_lock and private_list for
476  * whatever they want.  The only requirement is that list_empty(private_list)
477  * be true at clear_inode() time.
478  *
479  * FIXME: clear_inode should not call invalidate_inode_buffers().  The
480  * filesystems should do that.  invalidate_inode_buffers() should just go
481  * BUG_ON(!list_empty).
482  *
483  * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
484  * take an address_space, not an inode.  And it should be called
485  * mark_buffer_dirty_fsync() to clearly define why those buffers are being
486  * queued up.
487  *
488  * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
489  * list if it is already on a list.  Because if the buffer is on a list,
490  * it *must* already be on the right one.  If not, the filesystem is being
491  * silly.  This will save a ton of locking.  But first we have to ensure
492  * that buffers are taken *off* the old inode's list when they are freed
493  * (presumably in truncate).  That requires careful auditing of all
494  * filesystems (do it inside bforget()).  It could also be done by bringing
495  * b_inode back.
496  */
497
498 /*
499  * The buffer's backing address_space's private_lock must be held
500  */
501 static void __remove_assoc_queue(struct buffer_head *bh)
502 {
503         list_del_init(&bh->b_assoc_buffers);
504         WARN_ON(!bh->b_assoc_map);
505         if (buffer_write_io_error(bh))
506                 set_bit(AS_EIO, &bh->b_assoc_map->flags);
507         bh->b_assoc_map = NULL;
508 }
509
510 int inode_has_buffers(struct inode *inode)
511 {
512         return !list_empty(&inode->i_data.private_list);
513 }
514
515 /*
516  * osync is designed to support O_SYNC io.  It waits synchronously for
517  * all already-submitted IO to complete, but does not queue any new
518  * writes to the disk.
519  *
520  * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
521  * you dirty the buffers, and then use osync_inode_buffers to wait for
522  * completion.  Any other dirty buffers which are not yet queued for
523  * write will not be flushed to disk by the osync.
524  */
525 static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
526 {
527         struct buffer_head *bh;
528         struct list_head *p;
529         int err = 0;
530
531         spin_lock(lock);
532 repeat:
533         list_for_each_prev(p, list) {
534                 bh = BH_ENTRY(p);
535                 if (buffer_locked(bh)) {
536                         get_bh(bh);
537                         spin_unlock(lock);
538                         wait_on_buffer(bh);
539                         if (!buffer_uptodate(bh))
540                                 err = -EIO;
541                         brelse(bh);
542                         spin_lock(lock);
543                         goto repeat;
544                 }
545         }
546         spin_unlock(lock);
547         return err;
548 }
549
550 void do_thaw_all(unsigned long unused)
551 {
552         struct super_block *sb;
553         char b[BDEVNAME_SIZE];
554
555         spin_lock(&sb_lock);
556 restart:
557         list_for_each_entry(sb, &super_blocks, s_list) {
558                 sb->s_count++;
559                 spin_unlock(&sb_lock);
560                 down_read(&sb->s_umount);
561                 while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
562                         printk(KERN_WARNING "Emergency Thaw on %s\n",
563                                bdevname(sb->s_bdev, b));
564                 up_read(&sb->s_umount);
565                 spin_lock(&sb_lock);
566                 if (__put_super_and_need_restart(sb))
567                         goto restart;
568         }
569         spin_unlock(&sb_lock);
570         printk(KERN_WARNING "Emergency Thaw complete\n");
571 }
572
573 /**
574  * emergency_thaw_all -- forcibly thaw every frozen filesystem
575  *
576  * Used for emergency unfreeze of all filesystems via SysRq
577  */
578 void emergency_thaw_all(void)
579 {
580         pdflush_operation(do_thaw_all, 0);
581 }
582
583 /**
584  * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
585  * @mapping: the mapping which wants those buffers written
586  *
587  * Starts I/O against the buffers at mapping->private_list, and waits upon
588  * that I/O.
589  *
590  * Basically, this is a convenience function for fsync().
591  * @mapping is a file or directory which needs those buffers to be written for
592  * a successful fsync().
593  */
594 int sync_mapping_buffers(struct address_space *mapping)
595 {
596         struct address_space *buffer_mapping = mapping->assoc_mapping;
597
598         if (buffer_mapping == NULL || list_empty(&mapping->private_list))
599                 return 0;
600
601         return fsync_buffers_list(&buffer_mapping->private_lock,
602                                         &mapping->private_list);
603 }
604 EXPORT_SYMBOL(sync_mapping_buffers);
605
606 /*
607  * Called when we've recently written block `bblock', and it is known that
608  * `bblock' was for a buffer_boundary() buffer.  This means that the block at
609  * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
610  * dirty, schedule it for IO.  So that indirects merge nicely with their data.
611  */
612 void write_boundary_block(struct block_device *bdev,
613                         sector_t bblock, unsigned blocksize)
614 {
615         struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
616         if (bh) {
617                 if (buffer_dirty(bh))
618                         ll_rw_block(WRITE, 1, &bh);
619                 put_bh(bh);
620         }
621 }
622
623 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
624 {
625         struct address_space *mapping = inode->i_mapping;
626         struct address_space *buffer_mapping = bh->b_page->mapping;
627
628         mark_buffer_dirty(bh);
629         if (!mapping->assoc_mapping) {
630                 mapping->assoc_mapping = buffer_mapping;
631         } else {
632                 BUG_ON(mapping->assoc_mapping != buffer_mapping);
633         }
634         if (!bh->b_assoc_map) {
635                 spin_lock(&buffer_mapping->private_lock);
636                 list_move_tail(&bh->b_assoc_buffers,
637                                 &mapping->private_list);
638                 bh->b_assoc_map = mapping;
639                 spin_unlock(&buffer_mapping->private_lock);
640         }
641 }
642 EXPORT_SYMBOL(mark_buffer_dirty_inode);
643
644 /*
645  * Mark the page dirty, and set it dirty in the radix tree, and mark the inode
646  * dirty.
647  *
648  * If warn is true, then emit a warning if the page is not uptodate and has
649  * not been truncated.
650  */
651 static void __set_page_dirty(struct page *page,
652                 struct address_space *mapping, int warn)
653 {
654         spin_lock_irq(&mapping->tree_lock);
655         if (page->mapping) {    /* Race with truncate? */
656                 WARN_ON_ONCE(warn && !PageUptodate(page));
657                 account_page_dirtied(page, mapping);
658                 radix_tree_tag_set(&mapping->page_tree,
659                                 page_index(page), PAGECACHE_TAG_DIRTY);
660         }
661         spin_unlock_irq(&mapping->tree_lock);
662         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
663 }
664
665 /*
666  * Add a page to the dirty page list.
667  *
668  * It is a sad fact of life that this function is called from several places
669  * deeply under spinlocking.  It may not sleep.
670  *
671  * If the page has buffers, the uptodate buffers are set dirty, to preserve
672  * dirty-state coherency between the page and the buffers.  It the page does
673  * not have buffers then when they are later attached they will all be set
674  * dirty.
675  *
676  * The buffers are dirtied before the page is dirtied.  There's a small race
677  * window in which a writepage caller may see the page cleanness but not the
678  * buffer dirtiness.  That's fine.  If this code were to set the page dirty
679  * before the buffers, a concurrent writepage caller could clear the page dirty
680  * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
681  * page on the dirty page list.
682  *
683  * We use private_lock to lock against try_to_free_buffers while using the
684  * page's buffer list.  Also use this to protect against clean buffers being
685  * added to the page after it was set dirty.
686  *
687  * FIXME: may need to call ->reservepage here as well.  That's rather up to the
688  * address_space though.
689  */
690 int __set_page_dirty_buffers(struct page *page)
691 {
692         int newly_dirty;
693         struct address_space *mapping = page_mapping(page);
694
695         if (unlikely(!mapping))
696                 return !TestSetPageDirty(page);
697
698         spin_lock(&mapping->private_lock);
699         if (page_has_buffers(page)) {
700                 struct buffer_head *head = page_buffers(page);
701                 struct buffer_head *bh = head;
702
703                 do {
704                         set_buffer_dirty(bh);
705                         bh = bh->b_this_page;
706                 } while (bh != head);
707         }
708         newly_dirty = !TestSetPageDirty(page);
709         spin_unlock(&mapping->private_lock);
710
711         if (newly_dirty)
712                 __set_page_dirty(page, mapping, 1);
713         return newly_dirty;
714 }
715 EXPORT_SYMBOL(__set_page_dirty_buffers);
716
717 /*
718  * Write out and wait upon a list of buffers.
719  *
720  * We have conflicting pressures: we want to make sure that all
721  * initially dirty buffers get waited on, but that any subsequently
722  * dirtied buffers don't.  After all, we don't want fsync to last
723  * forever if somebody is actively writing to the file.
724  *
725  * Do this in two main stages: first we copy dirty buffers to a
726  * temporary inode list, queueing the writes as we go.  Then we clean
727  * up, waiting for those writes to complete.
728  * 
729  * During this second stage, any subsequent updates to the file may end
730  * up refiling the buffer on the original inode's dirty list again, so
731  * there is a chance we will end up with a buffer queued for write but
732  * not yet completed on that list.  So, as a final cleanup we go through
733  * the osync code to catch these locked, dirty buffers without requeuing
734  * any newly dirty buffers for write.
735  */
736 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
737 {
738         struct buffer_head *bh;
739         struct list_head tmp;
740         struct address_space *mapping;
741         int err = 0, err2;
742
743         INIT_LIST_HEAD(&tmp);
744
745         spin_lock(lock);
746         while (!list_empty(list)) {
747                 bh = BH_ENTRY(list->next);
748                 mapping = bh->b_assoc_map;
749                 __remove_assoc_queue(bh);
750                 /* Avoid race with mark_buffer_dirty_inode() which does
751                  * a lockless check and we rely on seeing the dirty bit */
752                 smp_mb();
753                 if (buffer_dirty(bh) || buffer_locked(bh)) {
754                         list_add(&bh->b_assoc_buffers, &tmp);
755                         bh->b_assoc_map = mapping;
756                         if (buffer_dirty(bh)) {
757                                 get_bh(bh);
758                                 spin_unlock(lock);
759                                 /*
760                                  * Ensure any pending I/O completes so that
761                                  * ll_rw_block() actually writes the current
762                                  * contents - it is a noop if I/O is still in
763                                  * flight on potentially older contents.
764                                  */
765                                 ll_rw_block(SWRITE_SYNC, 1, &bh);
766                                 brelse(bh);
767                                 spin_lock(lock);
768                         }
769                 }
770         }
771
772         while (!list_empty(&tmp)) {
773                 bh = BH_ENTRY(tmp.prev);
774                 get_bh(bh);
775                 mapping = bh->b_assoc_map;
776                 __remove_assoc_queue(bh);
777                 /* Avoid race with mark_buffer_dirty_inode() which does
778                  * a lockless check and we rely on seeing the dirty bit */
779                 smp_mb();
780                 if (buffer_dirty(bh)) {
781                         list_add(&bh->b_assoc_buffers,
782                                  &mapping->private_list);
783                         bh->b_assoc_map = mapping;
784                 }
785                 spin_unlock(lock);
786                 wait_on_buffer(bh);
787                 if (!buffer_uptodate(bh))
788                         err = -EIO;
789                 brelse(bh);
790                 spin_lock(lock);
791         }
792         
793         spin_unlock(lock);
794         err2 = osync_buffers_list(lock, list);
795         if (err)
796                 return err;
797         else
798                 return err2;
799 }
800
801 /*
802  * Invalidate any and all dirty buffers on a given inode.  We are
803  * probably unmounting the fs, but that doesn't mean we have already
804  * done a sync().  Just drop the buffers from the inode list.
805  *
806  * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
807  * assumes that all the buffers are against the blockdev.  Not true
808  * for reiserfs.
809  */
810 void invalidate_inode_buffers(struct inode *inode)
811 {
812         if (inode_has_buffers(inode)) {
813                 struct address_space *mapping = &inode->i_data;
814                 struct list_head *list = &mapping->private_list;
815                 struct address_space *buffer_mapping = mapping->assoc_mapping;
816
817                 spin_lock(&buffer_mapping->private_lock);
818                 while (!list_empty(list))
819                         __remove_assoc_queue(BH_ENTRY(list->next));
820                 spin_unlock(&buffer_mapping->private_lock);
821         }
822 }
823 EXPORT_SYMBOL(invalidate_inode_buffers);
824
825 /*
826  * Remove any clean buffers from the inode's buffer list.  This is called
827  * when we're trying to free the inode itself.  Those buffers can pin it.
828  *
829  * Returns true if all buffers were removed.
830  */
831 int remove_inode_buffers(struct inode *inode)
832 {
833         int ret = 1;
834
835         if (inode_has_buffers(inode)) {
836                 struct address_space *mapping = &inode->i_data;
837                 struct list_head *list = &mapping->private_list;
838                 struct address_space *buffer_mapping = mapping->assoc_mapping;
839
840                 spin_lock(&buffer_mapping->private_lock);
841                 while (!list_empty(list)) {
842                         struct buffer_head *bh = BH_ENTRY(list->next);
843                         if (buffer_dirty(bh)) {
844                                 ret = 0;
845                                 break;
846                         }
847                         __remove_assoc_queue(bh);
848                 }
849                 spin_unlock(&buffer_mapping->private_lock);
850         }
851         return ret;
852 }
853
854 /*
855  * Create the appropriate buffers when given a page for data area and
856  * the size of each buffer.. Use the bh->b_this_page linked list to
857  * follow the buffers created.  Return NULL if unable to create more
858  * buffers.
859  *
860  * The retry flag is used to differentiate async IO (paging, swapping)
861  * which may not fail from ordinary buffer allocations.
862  */
863 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
864                 int retry)
865 {
866         struct buffer_head *bh, *head;
867         long offset;
868
869 try_again:
870         head = NULL;
871         offset = PAGE_SIZE;
872         while ((offset -= size) >= 0) {
873                 bh = alloc_buffer_head(GFP_NOFS);
874                 if (!bh)
875                         goto no_grow;
876
877                 bh->b_bdev = NULL;
878                 bh->b_this_page = head;
879                 bh->b_blocknr = -1;
880                 head = bh;
881
882                 bh->b_state = 0;
883                 atomic_set(&bh->b_count, 0);
884                 bh->b_private = NULL;
885                 bh->b_size = size;
886
887                 /* Link the buffer to its page */
888                 set_bh_page(bh, page, offset);
889
890                 init_buffer(bh, NULL, NULL);
891         }
892         return head;
893 /*
894  * In case anything failed, we just free everything we got.
895  */
896 no_grow:
897         if (head) {
898                 do {
899                         bh = head;
900                         head = head->b_this_page;
901                         free_buffer_head(bh);
902                 } while (head);
903         }
904
905         /*
906          * Return failure for non-async IO requests.  Async IO requests
907          * are not allowed to fail, so we have to wait until buffer heads
908          * become available.  But we don't want tasks sleeping with 
909          * partially complete buffers, so all were released above.
910          */
911         if (!retry)
912                 return NULL;
913
914         /* We're _really_ low on memory. Now we just
915          * wait for old buffer heads to become free due to
916          * finishing IO.  Since this is an async request and
917          * the reserve list is empty, we're sure there are 
918          * async buffer heads in use.
919          */
920         free_more_memory();
921         goto try_again;
922 }
923 EXPORT_SYMBOL_GPL(alloc_page_buffers);
924
925 static inline void
926 link_dev_buffers(struct page *page, struct buffer_head *head)
927 {
928         struct buffer_head *bh, *tail;
929
930         bh = head;
931         do {
932                 tail = bh;
933                 bh = bh->b_this_page;
934         } while (bh);
935         tail->b_this_page = head;
936         attach_page_buffers(page, head);
937 }
938
939 /*
940  * Initialise the state of a blockdev page's buffers.
941  */ 
942 static void
943 init_page_buffers(struct page *page, struct block_device *bdev,
944                         sector_t block, int size)
945 {
946         struct buffer_head *head = page_buffers(page);
947         struct buffer_head *bh = head;
948         int uptodate = PageUptodate(page);
949
950         do {
951                 if (!buffer_mapped(bh)) {
952                         init_buffer(bh, NULL, NULL);
953                         bh->b_bdev = bdev;
954                         bh->b_blocknr = block;
955                         if (uptodate)
956                                 set_buffer_uptodate(bh);
957                         set_buffer_mapped(bh);
958                 }
959                 block++;
960                 bh = bh->b_this_page;
961         } while (bh != head);
962 }
963
964 /*
965  * Create the page-cache page that contains the requested block.
966  *
967  * This is user purely for blockdev mappings.
968  */
969 static struct page *
970 grow_dev_page(struct block_device *bdev, sector_t block,
971                 pgoff_t index, int size)
972 {
973         struct inode *inode = bdev->bd_inode;
974         struct page *page;
975         struct buffer_head *bh;
976
977         page = find_or_create_page(inode->i_mapping, index,
978                 (mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS)|__GFP_MOVABLE);
979         if (!page)
980                 return NULL;
981
982         BUG_ON(!PageLocked(page));
983
984         if (page_has_buffers(page)) {
985                 bh = page_buffers(page);
986                 if (bh->b_size == size) {
987                         init_page_buffers(page, bdev, block, size);
988                         return page;
989                 }
990                 if (!try_to_free_buffers(page))
991                         goto failed;
992         }
993
994         /*
995          * Allocate some buffers for this page
996          */
997         bh = alloc_page_buffers(page, size, 0);
998         if (!bh)
999                 goto failed;
1000
1001         /*
1002          * Link the page to the buffers and initialise them.  Take the
1003          * lock to be atomic wrt __find_get_block(), which does not
1004          * run under the page lock.
1005          */
1006         spin_lock(&inode->i_mapping->private_lock);
1007         link_dev_buffers(page, bh);
1008         init_page_buffers(page, bdev, block, size);
1009         spin_unlock(&inode->i_mapping->private_lock);
1010         return page;
1011
1012 failed:
1013         BUG();
1014         unlock_page(page);
1015         page_cache_release(page);
1016         return NULL;
1017 }
1018
1019 /*
1020  * Create buffers for the specified block device block's page.  If
1021  * that page was dirty, the buffers are set dirty also.
1022  */
1023 static int
1024 grow_buffers(struct block_device *bdev, sector_t block, int size)
1025 {
1026         struct page *page;
1027         pgoff_t index;
1028         int sizebits;
1029
1030         sizebits = -1;
1031         do {
1032                 sizebits++;
1033         } while ((size << sizebits) < PAGE_SIZE);
1034
1035         index = block >> sizebits;
1036
1037         /*
1038          * Check for a block which wants to lie outside our maximum possible
1039          * pagecache index.  (this comparison is done using sector_t types).
1040          */
1041         if (unlikely(index != block >> sizebits)) {
1042                 char b[BDEVNAME_SIZE];
1043
1044                 printk(KERN_ERR "%s: requested out-of-range block %llu for "
1045                         "device %s\n",
1046                         __func__, (unsigned long long)block,
1047                         bdevname(bdev, b));
1048                 return -EIO;
1049         }
1050         block = index << sizebits;
1051         /* Create a page with the proper size buffers.. */
1052         page = grow_dev_page(bdev, block, index, size);
1053         if (!page)
1054                 return 0;
1055         unlock_page(page);
1056         page_cache_release(page);
1057         return 1;
1058 }
1059
1060 static struct buffer_head *
1061 __getblk_slow(struct block_device *bdev, sector_t block, int size)
1062 {
1063         /* Size must be multiple of hard sectorsize */
1064         if (unlikely(size & (bdev_hardsect_size(bdev)-1) ||
1065                         (size < 512 || size > PAGE_SIZE))) {
1066                 printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1067                                         size);
1068                 printk(KERN_ERR "hardsect size: %d\n",
1069                                         bdev_hardsect_size(bdev));
1070
1071                 dump_stack();
1072                 return NULL;
1073         }
1074
1075         for (;;) {
1076                 struct buffer_head * bh;
1077                 int ret;
1078
1079                 bh = __find_get_block(bdev, block, size);
1080                 if (bh)
1081                         return bh;
1082
1083                 ret = grow_buffers(bdev, block, size);
1084                 if (ret < 0)
1085                         return NULL;
1086                 if (ret == 0)
1087                         free_more_memory();
1088         }
1089 }
1090
1091 /*
1092  * The relationship between dirty buffers and dirty pages:
1093  *
1094  * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1095  * the page is tagged dirty in its radix tree.
1096  *
1097  * At all times, the dirtiness of the buffers represents the dirtiness of
1098  * subsections of the page.  If the page has buffers, the page dirty bit is
1099  * merely a hint about the true dirty state.
1100  *
1101  * When a page is set dirty in its entirety, all its buffers are marked dirty
1102  * (if the page has buffers).
1103  *
1104  * When a buffer is marked dirty, its page is dirtied, but the page's other
1105  * buffers are not.
1106  *
1107  * Also.  When blockdev buffers are explicitly read with bread(), they
1108  * individually become uptodate.  But their backing page remains not
1109  * uptodate - even if all of its buffers are uptodate.  A subsequent
1110  * block_read_full_page() against that page will discover all the uptodate
1111  * buffers, will set the page uptodate and will perform no I/O.
1112  */
1113
1114 /**
1115  * mark_buffer_dirty - mark a buffer_head as needing writeout
1116  * @bh: the buffer_head to mark dirty
1117  *
1118  * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1119  * backing page dirty, then tag the page as dirty in its address_space's radix
1120  * tree and then attach the address_space's inode to its superblock's dirty
1121  * inode list.
1122  *
1123  * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1124  * mapping->tree_lock and the global inode_lock.
1125  */
1126 void mark_buffer_dirty(struct buffer_head *bh)
1127 {
1128         WARN_ON_ONCE(!buffer_uptodate(bh));
1129
1130         /*
1131          * Very *carefully* optimize the it-is-already-dirty case.
1132          *
1133          * Don't let the final "is it dirty" escape to before we
1134          * perhaps modified the buffer.
1135          */
1136         if (buffer_dirty(bh)) {
1137                 smp_mb();
1138                 if (buffer_dirty(bh))
1139                         return;
1140         }
1141
1142         if (!test_set_buffer_dirty(bh)) {
1143                 struct page *page = bh->b_page;
1144                 if (!TestSetPageDirty(page))
1145                         __set_page_dirty(page, page_mapping(page), 0);
1146         }
1147 }
1148
1149 /*
1150  * Decrement a buffer_head's reference count.  If all buffers against a page
1151  * have zero reference count, are clean and unlocked, and if the page is clean
1152  * and unlocked then try_to_free_buffers() may strip the buffers from the page
1153  * in preparation for freeing it (sometimes, rarely, buffers are removed from
1154  * a page but it ends up not being freed, and buffers may later be reattached).
1155  */
1156 void __brelse(struct buffer_head * buf)
1157 {
1158         if (atomic_read(&buf->b_count)) {
1159                 put_bh(buf);
1160                 return;
1161         }
1162         WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1163 }
1164
1165 /*
1166  * bforget() is like brelse(), except it discards any
1167  * potentially dirty data.
1168  */
1169 void __bforget(struct buffer_head *bh)
1170 {
1171         clear_buffer_dirty(bh);
1172         if (bh->b_assoc_map) {
1173                 struct address_space *buffer_mapping = bh->b_page->mapping;
1174
1175                 spin_lock(&buffer_mapping->private_lock);
1176                 list_del_init(&bh->b_assoc_buffers);
1177                 bh->b_assoc_map = NULL;
1178                 spin_unlock(&buffer_mapping->private_lock);
1179         }
1180         __brelse(bh);
1181 }
1182
1183 static struct buffer_head *__bread_slow(struct buffer_head *bh)
1184 {
1185         lock_buffer(bh);
1186         if (buffer_uptodate(bh)) {
1187                 unlock_buffer(bh);
1188                 return bh;
1189         } else {
1190                 get_bh(bh);
1191                 bh->b_end_io = end_buffer_read_sync;
1192                 submit_bh(READ, bh);
1193                 wait_on_buffer(bh);
1194                 if (buffer_uptodate(bh))
1195                         return bh;
1196         }
1197         brelse(bh);
1198         return NULL;
1199 }
1200
1201 /*
1202  * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1203  * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1204  * refcount elevated by one when they're in an LRU.  A buffer can only appear
1205  * once in a particular CPU's LRU.  A single buffer can be present in multiple
1206  * CPU's LRUs at the same time.
1207  *
1208  * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1209  * sb_find_get_block().
1210  *
1211  * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1212  * a local interrupt disable for that.
1213  */
1214
1215 #define BH_LRU_SIZE     8
1216
1217 struct bh_lru {
1218         struct buffer_head *bhs[BH_LRU_SIZE];
1219 };
1220
1221 static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1222
1223 #ifdef CONFIG_SMP
1224 #define bh_lru_lock()   local_irq_disable()
1225 #define bh_lru_unlock() local_irq_enable()
1226 #else
1227 #define bh_lru_lock()   preempt_disable()
1228 #define bh_lru_unlock() preempt_enable()
1229 #endif
1230
1231 static inline void check_irqs_on(void)
1232 {
1233 #ifdef irqs_disabled
1234         BUG_ON(irqs_disabled());
1235 #endif
1236 }
1237
1238 /*
1239  * The LRU management algorithm is dopey-but-simple.  Sorry.
1240  */
1241 static void bh_lru_install(struct buffer_head *bh)
1242 {
1243         struct buffer_head *evictee = NULL;
1244         struct bh_lru *lru;
1245
1246         check_irqs_on();
1247         bh_lru_lock();
1248         lru = &__get_cpu_var(bh_lrus);
1249         if (lru->bhs[0] != bh) {
1250                 struct buffer_head *bhs[BH_LRU_SIZE];
1251                 int in;
1252                 int out = 0;
1253
1254                 get_bh(bh);
1255                 bhs[out++] = bh;
1256                 for (in = 0; in < BH_LRU_SIZE; in++) {
1257                         struct buffer_head *bh2 = lru->bhs[in];
1258
1259                         if (bh2 == bh) {
1260                                 __brelse(bh2);
1261                         } else {
1262                                 if (out >= BH_LRU_SIZE) {
1263                                         BUG_ON(evictee != NULL);
1264                                         evictee = bh2;
1265                                 } else {
1266                                         bhs[out++] = bh2;
1267                                 }
1268                         }
1269                 }
1270                 while (out < BH_LRU_SIZE)
1271                         bhs[out++] = NULL;
1272                 memcpy(lru->bhs, bhs, sizeof(bhs));
1273         }
1274         bh_lru_unlock();
1275
1276         if (evictee)
1277                 __brelse(evictee);
1278 }
1279
1280 /*
1281  * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1282  */
1283 static struct buffer_head *
1284 lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1285 {
1286         struct buffer_head *ret = NULL;
1287         struct bh_lru *lru;
1288         unsigned int i;
1289
1290         check_irqs_on();
1291         bh_lru_lock();
1292         lru = &__get_cpu_var(bh_lrus);
1293         for (i = 0; i < BH_LRU_SIZE; i++) {
1294                 struct buffer_head *bh = lru->bhs[i];
1295
1296                 if (bh && bh->b_bdev == bdev &&
1297                                 bh->b_blocknr == block && bh->b_size == size) {
1298                         if (i) {
1299                                 while (i) {
1300                                         lru->bhs[i] = lru->bhs[i - 1];
1301                                         i--;
1302                                 }
1303                                 lru->bhs[0] = bh;
1304                         }
1305                         get_bh(bh);
1306                         ret = bh;
1307                         break;
1308                 }
1309         }
1310         bh_lru_unlock();
1311         return ret;
1312 }
1313
1314 /*
1315  * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1316  * it in the LRU and mark it as accessed.  If it is not present then return
1317  * NULL
1318  */
1319 struct buffer_head *
1320 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1321 {
1322         struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1323
1324         if (bh == NULL) {
1325                 bh = __find_get_block_slow(bdev, block);
1326                 if (bh)
1327                         bh_lru_install(bh);
1328         }
1329         if (bh)
1330                 touch_buffer(bh);
1331         return bh;
1332 }
1333 EXPORT_SYMBOL(__find_get_block);
1334
1335 /*
1336  * __getblk will locate (and, if necessary, create) the buffer_head
1337  * which corresponds to the passed block_device, block and size. The
1338  * returned buffer has its reference count incremented.
1339  *
1340  * __getblk() cannot fail - it just keeps trying.  If you pass it an
1341  * illegal block number, __getblk() will happily return a buffer_head
1342  * which represents the non-existent block.  Very weird.
1343  *
1344  * __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
1345  * attempt is failing.  FIXME, perhaps?
1346  */
1347 struct buffer_head *
1348 __getblk(struct block_device *bdev, sector_t block, unsigned size)
1349 {
1350         struct buffer_head *bh = __find_get_block(bdev, block, size);
1351
1352         might_sleep();
1353         if (bh == NULL)
1354                 bh = __getblk_slow(bdev, block, size);
1355         return bh;
1356 }
1357 EXPORT_SYMBOL(__getblk);
1358
1359 /*
1360  * Do async read-ahead on a buffer..
1361  */
1362 void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1363 {
1364         struct buffer_head *bh = __getblk(bdev, block, size);
1365         if (likely(bh)) {
1366                 ll_rw_block(READA, 1, &bh);
1367                 brelse(bh);
1368         }
1369 }
1370 EXPORT_SYMBOL(__breadahead);
1371
1372 /**
1373  *  __bread() - reads a specified block and returns the bh
1374  *  @bdev: the block_device to read from
1375  *  @block: number of block
1376  *  @size: size (in bytes) to read
1377  * 
1378  *  Reads a specified block, and returns buffer head that contains it.
1379  *  It returns NULL if the block was unreadable.
1380  */
1381 struct buffer_head *
1382 __bread(struct block_device *bdev, sector_t block, unsigned size)
1383 {
1384         struct buffer_head *bh = __getblk(bdev, block, size);
1385
1386         if (likely(bh) && !buffer_uptodate(bh))
1387                 bh = __bread_slow(bh);
1388         return bh;
1389 }
1390 EXPORT_SYMBOL(__bread);
1391
1392 /*
1393  * invalidate_bh_lrus() is called rarely - but not only at unmount.
1394  * This doesn't race because it runs in each cpu either in irq
1395  * or with preempt disabled.
1396  */
1397 static void invalidate_bh_lru(void *arg)
1398 {
1399         struct bh_lru *b = &get_cpu_var(bh_lrus);
1400         int i;
1401
1402         for (i = 0; i < BH_LRU_SIZE; i++) {
1403                 brelse(b->bhs[i]);
1404                 b->bhs[i] = NULL;
1405         }
1406         put_cpu_var(bh_lrus);
1407 }
1408         
1409 void invalidate_bh_lrus(void)
1410 {
1411         on_each_cpu(invalidate_bh_lru, NULL, 1);
1412 }
1413 EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1414
1415 void set_bh_page(struct buffer_head *bh,
1416                 struct page *page, unsigned long offset)
1417 {
1418         bh->b_page = page;
1419         BUG_ON(offset >= PAGE_SIZE);
1420         if (PageHighMem(page))
1421                 /*
1422                  * This catches illegal uses and preserves the offset:
1423                  */
1424                 bh->b_data = (char *)(0 + offset);
1425         else
1426                 bh->b_data = page_address(page) + offset;
1427 }
1428 EXPORT_SYMBOL(set_bh_page);
1429
1430 /*
1431  * Called when truncating a buffer on a page completely.
1432  */
1433 static void discard_buffer(struct buffer_head * bh)
1434 {
1435         lock_buffer(bh);
1436         clear_buffer_dirty(bh);
1437         bh->b_bdev = NULL;
1438         clear_buffer_mapped(bh);
1439         clear_buffer_req(bh);
1440         clear_buffer_new(bh);
1441         clear_buffer_delay(bh);
1442         clear_buffer_unwritten(bh);
1443         unlock_buffer(bh);
1444 }
1445
1446 /**
1447  * block_invalidatepage - invalidate part of all of a buffer-backed page
1448  *
1449  * @page: the page which is affected
1450  * @offset: the index of the truncation point
1451  *
1452  * block_invalidatepage() is called when all or part of the page has become
1453  * invalidatedby a truncate operation.
1454  *
1455  * block_invalidatepage() does not have to release all buffers, but it must
1456  * ensure that no dirty buffer is left outside @offset and that no I/O
1457  * is underway against any of the blocks which are outside the truncation
1458  * point.  Because the caller is about to free (and possibly reuse) those
1459  * blocks on-disk.
1460  */
1461 void block_invalidatepage(struct page *page, unsigned long offset)
1462 {
1463         struct buffer_head *head, *bh, *next;
1464         unsigned int curr_off = 0;
1465
1466         BUG_ON(!PageLocked(page));
1467         if (!page_has_buffers(page))
1468                 goto out;
1469
1470         head = page_buffers(page);
1471         bh = head;
1472         do {
1473                 unsigned int next_off = curr_off + bh->b_size;
1474                 next = bh->b_this_page;
1475
1476                 /*
1477                  * is this block fully invalidated?
1478                  */
1479                 if (offset <= curr_off)
1480                         discard_buffer(bh);
1481                 curr_off = next_off;
1482                 bh = next;
1483         } while (bh != head);
1484
1485         /*
1486          * We release buffers only if the entire page is being invalidated.
1487          * The get_block cached value has been unconditionally invalidated,
1488          * so real IO is not possible anymore.
1489          */
1490         if (offset == 0)
1491                 try_to_release_page(page, 0);
1492 out:
1493         return;
1494 }
1495 EXPORT_SYMBOL(block_invalidatepage);
1496
1497 /*
1498  * We attach and possibly dirty the buffers atomically wrt
1499  * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1500  * is already excluded via the page lock.
1501  */
1502 void create_empty_buffers(struct page *page,
1503                         unsigned long blocksize, unsigned long b_state)
1504 {
1505         struct buffer_head *bh, *head, *tail;
1506
1507         head = alloc_page_buffers(page, blocksize, 1);
1508         bh = head;
1509         do {
1510                 bh->b_state |= b_state;
1511                 tail = bh;
1512                 bh = bh->b_this_page;
1513         } while (bh);
1514         tail->b_this_page = head;
1515
1516         spin_lock(&page->mapping->private_lock);
1517         if (PageUptodate(page) || PageDirty(page)) {
1518                 bh = head;
1519                 do {
1520                         if (PageDirty(page))
1521                                 set_buffer_dirty(bh);
1522                         if (PageUptodate(page))
1523                                 set_buffer_uptodate(bh);
1524                         bh = bh->b_this_page;
1525                 } while (bh != head);
1526         }
1527         attach_page_buffers(page, head);
1528         spin_unlock(&page->mapping->private_lock);
1529 }
1530 EXPORT_SYMBOL(create_empty_buffers);
1531
1532 /*
1533  * We are taking a block for data and we don't want any output from any
1534  * buffer-cache aliases starting from return from that function and
1535  * until the moment when something will explicitly mark the buffer
1536  * dirty (hopefully that will not happen until we will free that block ;-)
1537  * We don't even need to mark it not-uptodate - nobody can expect
1538  * anything from a newly allocated buffer anyway. We used to used
1539  * unmap_buffer() for such invalidation, but that was wrong. We definitely
1540  * don't want to mark the alias unmapped, for example - it would confuse
1541  * anyone who might pick it with bread() afterwards...
1542  *
1543  * Also..  Note that bforget() doesn't lock the buffer.  So there can
1544  * be writeout I/O going on against recently-freed buffers.  We don't
1545  * wait on that I/O in bforget() - it's more efficient to wait on the I/O
1546  * only if we really need to.  That happens here.
1547  */
1548 void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1549 {
1550         struct buffer_head *old_bh;
1551
1552         might_sleep();
1553
1554         old_bh = __find_get_block_slow(bdev, block);
1555         if (old_bh) {
1556                 clear_buffer_dirty(old_bh);
1557                 wait_on_buffer(old_bh);
1558                 clear_buffer_req(old_bh);
1559                 __brelse(old_bh);
1560         }
1561 }
1562 EXPORT_SYMBOL(unmap_underlying_metadata);
1563
1564 /*
1565  * NOTE! All mapped/uptodate combinations are valid:
1566  *
1567  *      Mapped  Uptodate        Meaning
1568  *
1569  *      No      No              "unknown" - must do get_block()
1570  *      No      Yes             "hole" - zero-filled
1571  *      Yes     No              "allocated" - allocated on disk, not read in
1572  *      Yes     Yes             "valid" - allocated and up-to-date in memory.
1573  *
1574  * "Dirty" is valid only with the last case (mapped+uptodate).
1575  */
1576
1577 /*
1578  * While block_write_full_page is writing back the dirty buffers under
1579  * the page lock, whoever dirtied the buffers may decide to clean them
1580  * again at any time.  We handle that by only looking at the buffer
1581  * state inside lock_buffer().
1582  *
1583  * If block_write_full_page() is called for regular writeback
1584  * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1585  * locked buffer.   This only can happen if someone has written the buffer
1586  * directly, with submit_bh().  At the address_space level PageWriteback
1587  * prevents this contention from occurring.
1588  */
1589 static int __block_write_full_page(struct inode *inode, struct page *page,
1590                         get_block_t *get_block, struct writeback_control *wbc)
1591 {
1592         int err;
1593         sector_t block;
1594         sector_t last_block;
1595         struct buffer_head *bh, *head;
1596         const unsigned blocksize = 1 << inode->i_blkbits;
1597         int nr_underway = 0;
1598
1599         BUG_ON(!PageLocked(page));
1600
1601         last_block = (i_size_read(inode) - 1) >> inode->i_blkbits;
1602
1603         if (!page_has_buffers(page)) {
1604                 create_empty_buffers(page, blocksize,
1605                                         (1 << BH_Dirty)|(1 << BH_Uptodate));
1606         }
1607
1608         /*
1609          * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1610          * here, and the (potentially unmapped) buffers may become dirty at
1611          * any time.  If a buffer becomes dirty here after we've inspected it
1612          * then we just miss that fact, and the page stays dirty.
1613          *
1614          * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1615          * handle that here by just cleaning them.
1616          */
1617
1618         block = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
1619         head = page_buffers(page);
1620         bh = head;
1621
1622         /*
1623          * Get all the dirty buffers mapped to disk addresses and
1624          * handle any aliases from the underlying blockdev's mapping.
1625          */
1626         do {
1627                 if (block > last_block) {
1628                         /*
1629                          * mapped buffers outside i_size will occur, because
1630                          * this page can be outside i_size when there is a
1631                          * truncate in progress.
1632                          */
1633                         /*
1634                          * The buffer was zeroed by block_write_full_page()
1635                          */
1636                         clear_buffer_dirty(bh);
1637                         set_buffer_uptodate(bh);
1638                 } else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1639                            buffer_dirty(bh)) {
1640                         WARN_ON(bh->b_size != blocksize);
1641                         err = get_block(inode, block, bh, 1);
1642                         if (err)
1643                                 goto recover;
1644                         clear_buffer_delay(bh);
1645                         if (buffer_new(bh)) {
1646                                 /* blockdev mappings never come here */
1647                                 clear_buffer_new(bh);
1648                                 unmap_underlying_metadata(bh->b_bdev,
1649                                                         bh->b_blocknr);
1650                         }
1651                 }
1652                 bh = bh->b_this_page;
1653                 block++;
1654         } while (bh != head);
1655
1656         do {
1657                 if (!buffer_mapped(bh))
1658                         continue;
1659                 /*
1660                  * If it's a fully non-blocking write attempt and we cannot
1661                  * lock the buffer then redirty the page.  Note that this can
1662                  * potentially cause a busy-wait loop from pdflush and kswapd
1663                  * activity, but those code paths have their own higher-level
1664                  * throttling.
1665                  */
1666                 if (wbc->sync_mode != WB_SYNC_NONE || !wbc->nonblocking) {
1667                         lock_buffer(bh);
1668                 } else if (!trylock_buffer(bh)) {
1669                         redirty_page_for_writepage(wbc, page);
1670                         continue;
1671                 }
1672                 if (test_clear_buffer_dirty(bh)) {
1673                         mark_buffer_async_write(bh);
1674                 } else {
1675                         unlock_buffer(bh);
1676                 }
1677         } while ((bh = bh->b_this_page) != head);
1678
1679         /*
1680          * The page and its buffers are protected by PageWriteback(), so we can
1681          * drop the bh refcounts early.
1682          */
1683         BUG_ON(PageWriteback(page));
1684         set_page_writeback(page);
1685
1686         do {
1687                 struct buffer_head *next = bh->b_this_page;
1688                 if (buffer_async_write(bh)) {
1689                         submit_bh(WRITE, bh);
1690                         nr_underway++;
1691                 }
1692                 bh = next;
1693         } while (bh != head);
1694         unlock_page(page);
1695
1696         err = 0;
1697 done:
1698         if (nr_underway == 0) {
1699                 /*
1700                  * The page was marked dirty, but the buffers were
1701                  * clean.  Someone wrote them back by hand with
1702                  * ll_rw_block/submit_bh.  A rare case.
1703                  */
1704                 end_page_writeback(page);
1705
1706                 /*
1707                  * The page and buffer_heads can be released at any time from
1708                  * here on.
1709                  */
1710         }
1711         return err;
1712
1713 recover:
1714         /*
1715          * ENOSPC, or some other error.  We may already have added some
1716          * blocks to the file, so we need to write these out to avoid
1717          * exposing stale data.
1718          * The page is currently locked and not marked for writeback
1719          */
1720         bh = head;
1721         /* Recovery: lock and submit the mapped buffers */
1722         do {
1723                 if (buffer_mapped(bh) && buffer_dirty(bh) &&
1724                     !buffer_delay(bh)) {
1725                         lock_buffer(bh);
1726                         mark_buffer_async_write(bh);
1727                 } else {
1728                         /*
1729                          * The buffer may have been set dirty during
1730                          * attachment to a dirty page.
1731                          */
1732                         clear_buffer_dirty(bh);
1733                 }
1734         } while ((bh = bh->b_this_page) != head);
1735         SetPageError(page);
1736         BUG_ON(PageWriteback(page));
1737         mapping_set_error(page->mapping, err);
1738         set_page_writeback(page);
1739         do {
1740                 struct buffer_head *next = bh->b_this_page;
1741                 if (buffer_async_write(bh)) {
1742                         clear_buffer_dirty(bh);
1743                         submit_bh(WRITE, bh);
1744                         nr_underway++;
1745                 }
1746                 bh = next;
1747         } while (bh != head);
1748         unlock_page(page);
1749         goto done;
1750 }
1751
1752 /*
1753  * If a page has any new buffers, zero them out here, and mark them uptodate
1754  * and dirty so they'll be written out (in order to prevent uninitialised
1755  * block data from leaking). And clear the new bit.
1756  */
1757 void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1758 {
1759         unsigned int block_start, block_end;
1760         struct buffer_head *head, *bh;
1761
1762         BUG_ON(!PageLocked(page));
1763         if (!page_has_buffers(page))
1764                 return;
1765
1766         bh = head = page_buffers(page);
1767         block_start = 0;
1768         do {
1769                 block_end = block_start + bh->b_size;
1770
1771                 if (buffer_new(bh)) {
1772                         if (block_end > from && block_start < to) {
1773                                 if (!PageUptodate(page)) {
1774                                         unsigned start, size;
1775
1776                                         start = max(from, block_start);
1777                                         size = min(to, block_end) - start;
1778
1779                                         zero_user(page, start, size);
1780                                         set_buffer_uptodate(bh);
1781                                 }
1782
1783                                 clear_buffer_new(bh);
1784                                 mark_buffer_dirty(bh);
1785                         }
1786                 }
1787
1788                 block_start = block_end;
1789                 bh = bh->b_this_page;
1790         } while (bh != head);
1791 }
1792 EXPORT_SYMBOL(page_zero_new_buffers);
1793
1794 static int __block_prepare_write(struct inode *inode, struct page *page,
1795                 unsigned from, unsigned to, get_block_t *get_block)
1796 {
1797         unsigned block_start, block_end;
1798         sector_t block;
1799         int err = 0;
1800         unsigned blocksize, bbits;
1801         struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1802
1803         BUG_ON(!PageLocked(page));
1804         BUG_ON(from > PAGE_CACHE_SIZE);
1805         BUG_ON(to > PAGE_CACHE_SIZE);
1806         BUG_ON(from > to);
1807
1808         blocksize = 1 << inode->i_blkbits;
1809         if (!page_has_buffers(page))
1810                 create_empty_buffers(page, blocksize, 0);
1811         head = page_buffers(page);
1812
1813         bbits = inode->i_blkbits;
1814         block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1815
1816         for(bh = head, block_start = 0; bh != head || !block_start;
1817             block++, block_start=block_end, bh = bh->b_this_page) {
1818                 block_end = block_start + blocksize;
1819                 if (block_end <= from || block_start >= to) {
1820                         if (PageUptodate(page)) {
1821                                 if (!buffer_uptodate(bh))
1822                                         set_buffer_uptodate(bh);
1823                         }
1824                         continue;
1825                 }
1826                 if (buffer_new(bh))
1827                         clear_buffer_new(bh);
1828                 if (!buffer_mapped(bh)) {
1829                         WARN_ON(bh->b_size != blocksize);
1830                         err = get_block(inode, block, bh, 1);
1831                         if (err)
1832                                 break;
1833                         if (buffer_new(bh)) {
1834                                 unmap_underlying_metadata(bh->b_bdev,
1835                                                         bh->b_blocknr);
1836                                 if (PageUptodate(page)) {
1837                                         clear_buffer_new(bh);
1838                                         set_buffer_uptodate(bh);
1839                                         mark_buffer_dirty(bh);
1840                                         continue;
1841                                 }
1842                                 if (block_end > to || block_start < from)
1843                                         zero_user_segments(page,
1844                                                 to, block_end,
1845                                                 block_start, from);
1846                                 continue;
1847                         }
1848                 }
1849                 if (PageUptodate(page)) {
1850                         if (!buffer_uptodate(bh))
1851                                 set_buffer_uptodate(bh);
1852                         continue; 
1853                 }
1854                 if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1855                     !buffer_unwritten(bh) &&
1856                      (block_start < from || block_end > to)) {
1857                         ll_rw_block(READ, 1, &bh);
1858                         *wait_bh++=bh;
1859                 }
1860         }
1861         /*
1862          * If we issued read requests - let them complete.
1863          */
1864         while(wait_bh > wait) {
1865                 wait_on_buffer(*--wait_bh);
1866                 if (!buffer_uptodate(*wait_bh))
1867                         err = -EIO;
1868         }
1869         if (unlikely(err))
1870                 page_zero_new_buffers(page, from, to);
1871         return err;
1872 }
1873
1874 static int __block_commit_write(struct inode *inode, struct page *page,
1875                 unsigned from, unsigned to)
1876 {
1877         unsigned block_start, block_end;
1878         int partial = 0;
1879         unsigned blocksize;
1880         struct buffer_head *bh, *head;
1881
1882         blocksize = 1 << inode->i_blkbits;
1883
1884         for(bh = head = page_buffers(page), block_start = 0;
1885             bh != head || !block_start;
1886             block_start=block_end, bh = bh->b_this_page) {
1887                 block_end = block_start + blocksize;
1888                 if (block_end <= from || block_start >= to) {
1889                         if (!buffer_uptodate(bh))
1890                                 partial = 1;
1891                 } else {
1892                         set_buffer_uptodate(bh);
1893                         mark_buffer_dirty(bh);
1894                 }
1895                 clear_buffer_new(bh);
1896         }
1897
1898         /*
1899          * If this is a partial write which happened to make all buffers
1900          * uptodate then we can optimize away a bogus readpage() for
1901          * the next read(). Here we 'discover' whether the page went
1902          * uptodate as a result of this (potentially partial) write.
1903          */
1904         if (!partial)
1905                 SetPageUptodate(page);
1906         return 0;
1907 }
1908
1909 /*
1910  * block_write_begin takes care of the basic task of block allocation and
1911  * bringing partial write blocks uptodate first.
1912  *
1913  * If *pagep is not NULL, then block_write_begin uses the locked page
1914  * at *pagep rather than allocating its own. In this case, the page will
1915  * not be unlocked or deallocated on failure.
1916  */
1917 int block_write_begin(struct file *file, struct address_space *mapping,
1918                         loff_t pos, unsigned len, unsigned flags,
1919                         struct page **pagep, void **fsdata,
1920                         get_block_t *get_block)
1921 {
1922         struct inode *inode = mapping->host;
1923         int status = 0;
1924         struct page *page;
1925         pgoff_t index;
1926         unsigned start, end;
1927         int ownpage = 0;
1928
1929         index = pos >> PAGE_CACHE_SHIFT;
1930         start = pos & (PAGE_CACHE_SIZE - 1);
1931         end = start + len;
1932
1933         page = *pagep;
1934         if (page == NULL) {
1935                 ownpage = 1;
1936                 page = grab_cache_page_write_begin(mapping, index, flags);
1937                 if (!page) {
1938                         status = -ENOMEM;
1939                         goto out;
1940                 }
1941                 *pagep = page;
1942         } else
1943                 BUG_ON(!PageLocked(page));
1944
1945         status = __block_prepare_write(inode, page, start, end, get_block);
1946         if (unlikely(status)) {
1947                 ClearPageUptodate(page);
1948
1949                 if (ownpage) {
1950                         unlock_page(page);
1951                         page_cache_release(page);
1952                         *pagep = NULL;
1953
1954                         /*
1955                          * prepare_write() may have instantiated a few blocks
1956                          * outside i_size.  Trim these off again. Don't need
1957                          * i_size_read because we hold i_mutex.
1958                          */
1959                         if (pos + len > inode->i_size)
1960                                 vmtruncate(inode, inode->i_size);
1961                 }
1962         }
1963
1964 out:
1965         return status;
1966 }
1967 EXPORT_SYMBOL(block_write_begin);
1968
1969 int block_write_end(struct file *file, struct address_space *mapping,
1970                         loff_t pos, unsigned len, unsigned copied,
1971                         struct page *page, void *fsdata)
1972 {
1973         struct inode *inode = mapping->host;
1974         unsigned start;
1975
1976         start = pos & (PAGE_CACHE_SIZE - 1);
1977
1978         if (unlikely(copied < len)) {
1979                 /*
1980                  * The buffers that were written will now be uptodate, so we
1981                  * don't have to worry about a readpage reading them and
1982                  * overwriting a partial write. However if we have encountered
1983                  * a short write and only partially written into a buffer, it
1984                  * will not be marked uptodate, so a readpage might come in and
1985                  * destroy our partial write.
1986                  *
1987                  * Do the simplest thing, and just treat any short write to a
1988                  * non uptodate page as a zero-length write, and force the
1989                  * caller to redo the whole thing.
1990                  */
1991                 if (!PageUptodate(page))
1992                         copied = 0;
1993
1994                 page_zero_new_buffers(page, start+copied, start+len);
1995         }
1996         flush_dcache_page(page);
1997
1998         /* This could be a short (even 0-length) commit */
1999         __block_commit_write(inode, page, start, start+copied);
2000
2001         return copied;
2002 }
2003 EXPORT_SYMBOL(block_write_end);
2004
2005 int generic_write_end(struct file *file, struct address_space *mapping,
2006                         loff_t pos, unsigned len, unsigned copied,
2007                         struct page *page, void *fsdata)
2008 {
2009         struct inode *inode = mapping->host;
2010         int i_size_changed = 0;
2011
2012         copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2013
2014         /*
2015          * No need to use i_size_read() here, the i_size
2016          * cannot change under us because we hold i_mutex.
2017          *
2018          * But it's important to update i_size while still holding page lock:
2019          * page writeout could otherwise come in and zero beyond i_size.
2020          */
2021         if (pos+copied > inode->i_size) {
2022                 i_size_write(inode, pos+copied);
2023                 i_size_changed = 1;
2024         }
2025
2026         unlock_page(page);
2027         page_cache_release(page);
2028
2029         /*
2030          * Don't mark the inode dirty under page lock. First, it unnecessarily
2031          * makes the holding time of page lock longer. Second, it forces lock
2032          * ordering of page lock and transaction start for journaling
2033          * filesystems.
2034          */
2035         if (i_size_changed)
2036                 mark_inode_dirty(inode);
2037
2038         return copied;
2039 }
2040 EXPORT_SYMBOL(generic_write_end);
2041
2042 /*
2043  * block_is_partially_uptodate checks whether buffers within a page are
2044  * uptodate or not.
2045  *
2046  * Returns true if all buffers which correspond to a file portion
2047  * we want to read are uptodate.
2048  */
2049 int block_is_partially_uptodate(struct page *page, read_descriptor_t *desc,
2050                                         unsigned long from)
2051 {
2052         struct inode *inode = page->mapping->host;
2053         unsigned block_start, block_end, blocksize;
2054         unsigned to;
2055         struct buffer_head *bh, *head;
2056         int ret = 1;
2057
2058         if (!page_has_buffers(page))
2059                 return 0;
2060
2061         blocksize = 1 << inode->i_blkbits;
2062         to = min_t(unsigned, PAGE_CACHE_SIZE - from, desc->count);
2063         to = from + to;
2064         if (from < blocksize && to > PAGE_CACHE_SIZE - blocksize)
2065                 return 0;
2066
2067         head = page_buffers(page);
2068         bh = head;
2069         block_start = 0;
2070         do {
2071                 block_end = block_start + blocksize;
2072                 if (block_end > from && block_start < to) {
2073                         if (!buffer_uptodate(bh)) {
2074                                 ret = 0;
2075                                 break;
2076                         }
2077                         if (block_end >= to)
2078                                 break;
2079                 }
2080                 block_start = block_end;
2081                 bh = bh->b_this_page;
2082         } while (bh != head);
2083
2084         return ret;
2085 }
2086 EXPORT_SYMBOL(block_is_partially_uptodate);
2087
2088 /*
2089  * Generic "read page" function for block devices that have the normal
2090  * get_block functionality. This is most of the block device filesystems.
2091  * Reads the page asynchronously --- the unlock_buffer() and
2092  * set/clear_buffer_uptodate() functions propagate buffer state into the
2093  * page struct once IO has completed.
2094  */
2095 int block_read_full_page(struct page *page, get_block_t *get_block)
2096 {
2097         struct inode *inode = page->mapping->host;
2098         sector_t iblock, lblock;
2099         struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2100         unsigned int blocksize;
2101         int nr, i;
2102         int fully_mapped = 1;
2103
2104         BUG_ON(!PageLocked(page));
2105         blocksize = 1 << inode->i_blkbits;
2106         if (!page_has_buffers(page))
2107                 create_empty_buffers(page, blocksize, 0);
2108         head = page_buffers(page);
2109
2110         iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2111         lblock = (i_size_read(inode)+blocksize-1) >> inode->i_blkbits;
2112         bh = head;
2113         nr = 0;
2114         i = 0;
2115
2116         do {
2117                 if (buffer_uptodate(bh))
2118                         continue;
2119
2120                 if (!buffer_mapped(bh)) {
2121                         int err = 0;
2122
2123                         fully_mapped = 0;
2124                         if (iblock < lblock) {
2125                                 WARN_ON(bh->b_size != blocksize);
2126                                 err = get_block(inode, iblock, bh, 0);
2127                                 if (err)
2128                                         SetPageError(page);
2129                         }
2130                         if (!buffer_mapped(bh)) {
2131                                 zero_user(page, i * blocksize, blocksize);
2132                                 if (!err)
2133                                         set_buffer_uptodate(bh);
2134                                 continue;
2135                         }
2136                         /*
2137                          * get_block() might have updated the buffer
2138                          * synchronously
2139                          */
2140                         if (buffer_uptodate(bh))
2141                                 continue;
2142                 }
2143                 arr[nr++] = bh;
2144         } while (i++, iblock++, (bh = bh->b_this_page) != head);
2145
2146         if (fully_mapped)
2147                 SetPageMappedToDisk(page);
2148
2149         if (!nr) {
2150                 /*
2151                  * All buffers are uptodate - we can set the page uptodate
2152                  * as well. But not if get_block() returned an error.
2153                  */
2154                 if (!PageError(page))
2155                         SetPageUptodate(page);
2156                 unlock_page(page);
2157                 return 0;
2158         }
2159
2160         /* Stage two: lock the buffers */
2161         for (i = 0; i < nr; i++) {
2162                 bh = arr[i];
2163                 lock_buffer(bh);
2164                 mark_buffer_async_read(bh);
2165         }
2166
2167         /*
2168          * Stage 3: start the IO.  Check for uptodateness
2169          * inside the buffer lock in case another process reading
2170          * the underlying blockdev brought it uptodate (the sct fix).
2171          */
2172         for (i = 0; i < nr; i++) {
2173                 bh = arr[i];
2174                 if (buffer_uptodate(bh))
2175                         end_buffer_async_read(bh, 1);
2176                 else
2177                         submit_bh(READ, bh);
2178         }
2179         return 0;
2180 }
2181
2182 /* utility function for filesystems that need to do work on expanding
2183  * truncates.  Uses filesystem pagecache writes to allow the filesystem to
2184  * deal with the hole.  
2185  */
2186 int generic_cont_expand_simple(struct inode *inode, loff_t size)
2187 {
2188         struct address_space *mapping = inode->i_mapping;
2189         struct page *page;
2190         void *fsdata;
2191         unsigned long limit;
2192         int err;
2193
2194         err = -EFBIG;
2195         limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
2196         if (limit != RLIM_INFINITY && size > (loff_t)limit) {
2197                 send_sig(SIGXFSZ, current, 0);
2198                 goto out;
2199         }
2200         if (size > inode->i_sb->s_maxbytes)
2201                 goto out;
2202
2203         err = pagecache_write_begin(NULL, mapping, size, 0,
2204                                 AOP_FLAG_UNINTERRUPTIBLE|AOP_FLAG_CONT_EXPAND,
2205                                 &page, &fsdata);
2206         if (err)
2207                 goto out;
2208
2209         err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2210         BUG_ON(err > 0);
2211
2212 out:
2213         return err;
2214 }
2215
2216 static int cont_expand_zero(struct file *file, struct address_space *mapping,
2217                             loff_t pos, loff_t *bytes)
2218 {
2219         struct inode *inode = mapping->host;
2220         unsigned blocksize = 1 << inode->i_blkbits;
2221         struct page *page;
2222         void *fsdata;
2223         pgoff_t index, curidx;
2224         loff_t curpos;
2225         unsigned zerofrom, offset, len;
2226         int err = 0;
2227
2228         index = pos >> PAGE_CACHE_SHIFT;
2229         offset = pos & ~PAGE_CACHE_MASK;
2230
2231         while (index > (curidx = (curpos = *bytes)>>PAGE_CACHE_SHIFT)) {
2232                 zerofrom = curpos & ~PAGE_CACHE_MASK;
2233                 if (zerofrom & (blocksize-1)) {
2234                         *bytes |= (blocksize-1);
2235                         (*bytes)++;
2236                 }
2237                 len = PAGE_CACHE_SIZE - zerofrom;
2238
2239                 err = pagecache_write_begin(file, mapping, curpos, len,
2240                                                 AOP_FLAG_UNINTERRUPTIBLE,
2241                                                 &page, &fsdata);
2242                 if (err)
2243                         goto out;
2244                 zero_user(page, zerofrom, len);
2245                 err = pagecache_write_end(file, mapping, curpos, len, len,
2246                                                 page, fsdata);
2247                 if (err < 0)
2248                         goto out;
2249                 BUG_ON(err != len);
2250                 err = 0;
2251
2252                 balance_dirty_pages_ratelimited(mapping);
2253         }
2254
2255         /* page covers the boundary, find the boundary offset */
2256         if (index == curidx) {
2257                 zerofrom = curpos & ~PAGE_CACHE_MASK;
2258                 /* if we will expand the thing last block will be filled */
2259                 if (offset <= zerofrom) {
2260                         goto out;
2261                 }
2262                 if (zerofrom & (blocksize-1)) {
2263                         *bytes |= (blocksize-1);
2264                         (*bytes)++;
2265                 }
2266                 len = offset - zerofrom;
2267
2268                 err = pagecache_write_begin(file, mapping, curpos, len,
2269                                                 AOP_FLAG_UNINTERRUPTIBLE,
2270                                                 &page, &fsdata);
2271                 if (err)
2272                         goto out;
2273                 zero_user(page, zerofrom, len);
2274                 err = pagecache_write_end(file, mapping, curpos, len, len,
2275                                                 page, fsdata);
2276                 if (err < 0)
2277                         goto out;
2278                 BUG_ON(err != len);
2279                 err = 0;
2280         }
2281 out:
2282         return err;
2283 }
2284
2285 /*
2286  * For moronic filesystems that do not allow holes in file.
2287  * We may have to extend the file.
2288  */
2289 int cont_write_begin(struct file *file, struct address_space *mapping,
2290                         loff_t pos, unsigned len, unsigned flags,
2291                         struct page **pagep, void **fsdata,
2292                         get_block_t *get_block, loff_t *bytes)
2293 {
2294         struct inode *inode = mapping->host;
2295         unsigned blocksize = 1 << inode->i_blkbits;
2296         unsigned zerofrom;
2297         int err;
2298
2299         err = cont_expand_zero(file, mapping, pos, bytes);
2300         if (err)
2301                 goto out;
2302
2303         zerofrom = *bytes & ~PAGE_CACHE_MASK;
2304         if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2305                 *bytes |= (blocksize-1);
2306                 (*bytes)++;
2307         }
2308
2309         *pagep = NULL;
2310         err = block_write_begin(file, mapping, pos, len,
2311                                 flags, pagep, fsdata, get_block);
2312 out:
2313         return err;
2314 }
2315
2316 int block_prepare_write(struct page *page, unsigned from, unsigned to,
2317                         get_block_t *get_block)
2318 {
2319         struct inode *inode = page->mapping->host;
2320         int err = __block_prepare_write(inode, page, from, to, get_block);
2321         if (err)
2322                 ClearPageUptodate(page);
2323         return err;
2324 }
2325
2326 int block_commit_write(struct page *page, unsigned from, unsigned to)
2327 {
2328         struct inode *inode = page->mapping->host;
2329         __block_commit_write(inode,page,from,to);
2330         return 0;
2331 }
2332
2333 /*
2334  * block_page_mkwrite() is not allowed to change the file size as it gets
2335  * called from a page fault handler when a page is first dirtied. Hence we must
2336  * be careful to check for EOF conditions here. We set the page up correctly
2337  * for a written page which means we get ENOSPC checking when writing into
2338  * holes and correct delalloc and unwritten extent mapping on filesystems that
2339  * support these features.
2340  *
2341  * We are not allowed to take the i_mutex here so we have to play games to
2342  * protect against truncate races as the page could now be beyond EOF.  Because
2343  * vmtruncate() writes the inode size before removing pages, once we have the
2344  * page lock we can determine safely if the page is beyond EOF. If it is not
2345  * beyond EOF, then the page is guaranteed safe against truncation until we
2346  * unlock the page.
2347  */
2348 int
2349 block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2350                    get_block_t get_block)
2351 {
2352         struct page *page = vmf->page;
2353         struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
2354         unsigned long end;
2355         loff_t size;
2356         int ret = VM_FAULT_NOPAGE; /* make the VM retry the fault */
2357
2358         lock_page(page);
2359         size = i_size_read(inode);
2360         if ((page->mapping != inode->i_mapping) ||
2361             (page_offset(page) > size)) {
2362                 /* page got truncated out from underneath us */
2363                 goto out_unlock;
2364         }
2365
2366         /* page is wholly or partially inside EOF */
2367         if (((page->index + 1) << PAGE_CACHE_SHIFT) > size)
2368                 end = size & ~PAGE_CACHE_MASK;
2369         else
2370                 end = PAGE_CACHE_SIZE;
2371
2372         ret = block_prepare_write(page, 0, end, get_block);
2373         if (!ret)
2374                 ret = block_commit_write(page, 0, end);
2375
2376         if (unlikely(ret)) {
2377                 if (ret == -ENOMEM)
2378                         ret = VM_FAULT_OOM;
2379                 else /* -ENOSPC, -EIO, etc */
2380                         ret = VM_FAULT_SIGBUS;
2381         }
2382
2383 out_unlock:
2384         unlock_page(page);
2385         return ret;
2386 }
2387
2388 /*
2389  * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2390  * immediately, while under the page lock.  So it needs a special end_io
2391  * handler which does not touch the bh after unlocking it.
2392  */
2393 static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2394 {
2395         __end_buffer_read_notouch(bh, uptodate);
2396 }
2397
2398 /*
2399  * Attach the singly-linked list of buffers created by nobh_write_begin, to
2400  * the page (converting it to circular linked list and taking care of page
2401  * dirty races).
2402  */
2403 static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2404 {
2405         struct buffer_head *bh;
2406
2407         BUG_ON(!PageLocked(page));
2408
2409         spin_lock(&page->mapping->private_lock);
2410         bh = head;
2411         do {
2412                 if (PageDirty(page))
2413                         set_buffer_dirty(bh);
2414                 if (!bh->b_this_page)
2415                         bh->b_this_page = head;
2416                 bh = bh->b_this_page;
2417         } while (bh != head);
2418         attach_page_buffers(page, head);
2419         spin_unlock(&page->mapping->private_lock);
2420 }
2421
2422 /*
2423  * On entry, the page is fully not uptodate.
2424  * On exit the page is fully uptodate in the areas outside (from,to)
2425  */
2426 int nobh_write_begin(struct file *file, struct address_space *mapping,
2427                         loff_t pos, unsigned len, unsigned flags,
2428                         struct page **pagep, void **fsdata,
2429                         get_block_t *get_block)
2430 {
2431         struct inode *inode = mapping->host;
2432         const unsigned blkbits = inode->i_blkbits;
2433         const unsigned blocksize = 1 << blkbits;
2434         struct buffer_head *head, *bh;
2435         struct page *page;
2436         pgoff_t index;
2437         unsigned from, to;
2438         unsigned block_in_page;
2439         unsigned block_start, block_end;
2440         sector_t block_in_file;
2441         int nr_reads = 0;
2442         int ret = 0;
2443         int is_mapped_to_disk = 1;
2444
2445         index = pos >> PAGE_CACHE_SHIFT;
2446         from = pos & (PAGE_CACHE_SIZE - 1);
2447         to = from + len;
2448
2449         page = grab_cache_page_write_begin(mapping, index, flags);
2450         if (!page)
2451                 return -ENOMEM;
2452         *pagep = page;
2453         *fsdata = NULL;
2454
2455         if (page_has_buffers(page)) {
2456                 unlock_page(page);
2457                 page_cache_release(page);
2458                 *pagep = NULL;
2459                 return block_write_begin(file, mapping, pos, len, flags, pagep,
2460                                         fsdata, get_block);
2461         }
2462
2463         if (PageMappedToDisk(page))
2464                 return 0;
2465
2466         /*
2467          * Allocate buffers so that we can keep track of state, and potentially
2468          * attach them to the page if an error occurs. In the common case of
2469          * no error, they will just be freed again without ever being attached
2470          * to the page (which is all OK, because we're under the page lock).
2471          *
2472          * Be careful: the buffer linked list is a NULL terminated one, rather
2473          * than the circular one we're used to.
2474          */
2475         head = alloc_page_buffers(page, blocksize, 0);
2476         if (!head) {
2477                 ret = -ENOMEM;
2478                 goto out_release;
2479         }
2480
2481         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
2482
2483         /*
2484          * We loop across all blocks in the page, whether or not they are
2485          * part of the affected region.  This is so we can discover if the
2486          * page is fully mapped-to-disk.
2487          */
2488         for (block_start = 0, block_in_page = 0, bh = head;
2489                   block_start < PAGE_CACHE_SIZE;
2490                   block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2491                 int create;
2492
2493                 block_end = block_start + blocksize;
2494                 bh->b_state = 0;
2495                 create = 1;
2496                 if (block_start >= to)
2497                         create = 0;
2498                 ret = get_block(inode, block_in_file + block_in_page,
2499                                         bh, create);
2500                 if (ret)
2501                         goto failed;
2502                 if (!buffer_mapped(bh))
2503                         is_mapped_to_disk = 0;
2504                 if (buffer_new(bh))
2505                         unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
2506                 if (PageUptodate(page)) {
2507                         set_buffer_uptodate(bh);
2508                         continue;
2509                 }
2510                 if (buffer_new(bh) || !buffer_mapped(bh)) {
2511                         zero_user_segments(page, block_start, from,
2512                                                         to, block_end);
2513                         continue;
2514                 }
2515                 if (buffer_uptodate(bh))
2516                         continue;       /* reiserfs does this */
2517                 if (block_start < from || block_end > to) {
2518                         lock_buffer(bh);
2519                         bh->b_end_io = end_buffer_read_nobh;
2520                         submit_bh(READ, bh);
2521                         nr_reads++;
2522                 }
2523         }
2524
2525         if (nr_reads) {
2526                 /*
2527                  * The page is locked, so these buffers are protected from
2528                  * any VM or truncate activity.  Hence we don't need to care
2529                  * for the buffer_head refcounts.
2530                  */
2531                 for (bh = head; bh; bh = bh->b_this_page) {
2532                         wait_on_buffer(bh);
2533                         if (!buffer_uptodate(bh))
2534                                 ret = -EIO;
2535                 }
2536                 if (ret)
2537                         goto failed;
2538         }
2539
2540         if (is_mapped_to_disk)
2541                 SetPageMappedToDisk(page);
2542
2543         *fsdata = head; /* to be released by nobh_write_end */
2544
2545         return 0;
2546
2547 failed:
2548         BUG_ON(!ret);
2549         /*
2550          * Error recovery is a bit difficult. We need to zero out blocks that
2551          * were newly allocated, and dirty them to ensure they get written out.
2552          * Buffers need to be attached to the page at this point, otherwise
2553          * the handling of potential IO errors during writeout would be hard
2554          * (could try doing synchronous writeout, but what if that fails too?)
2555          */
2556         attach_nobh_buffers(page, head);
2557         page_zero_new_buffers(page, from, to);
2558
2559 out_release:
2560         unlock_page(page);
2561         page_cache_release(page);
2562         *pagep = NULL;
2563
2564         if (pos + len > inode->i_size)
2565                 vmtruncate(inode, inode->i_size);
2566
2567         return ret;
2568 }
2569 EXPORT_SYMBOL(nobh_write_begin);
2570
2571 int nobh_write_end(struct file *file, struct address_space *mapping,
2572                         loff_t pos, unsigned len, unsigned copied,
2573                         struct page *page, void *fsdata)
2574 {
2575         struct inode *inode = page->mapping->host;
2576         struct buffer_head *head = fsdata;
2577         struct buffer_head *bh;
2578         BUG_ON(fsdata != NULL && page_has_buffers(page));
2579
2580         if (unlikely(copied < len) && head)
2581                 attach_nobh_buffers(page, head);
2582         if (page_has_buffers(page))
2583                 return generic_write_end(file, mapping, pos, len,
2584                                         copied, page, fsdata);
2585
2586         SetPageUptodate(page);
2587         set_page_dirty(page);
2588         if (pos+copied > inode->i_size) {
2589                 i_size_write(inode, pos+copied);
2590                 mark_inode_dirty(inode);
2591         }
2592
2593         unlock_page(page);
2594         page_cache_release(page);
2595
2596         while (head) {
2597                 bh = head;
2598                 head = head->b_this_page;
2599                 free_buffer_head(bh);
2600         }
2601
2602         return copied;
2603 }
2604 EXPORT_SYMBOL(nobh_write_end);
2605
2606 /*
2607  * nobh_writepage() - based on block_full_write_page() except
2608  * that it tries to operate without attaching bufferheads to
2609  * the page.
2610  */
2611 int nobh_writepage(struct page *page, get_block_t *get_block,
2612                         struct writeback_control *wbc)
2613 {
2614         struct inode * const inode = page->mapping->host;
2615         loff_t i_size = i_size_read(inode);
2616         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2617         unsigned offset;
2618         int ret;
2619
2620         /* Is the page fully inside i_size? */
2621         if (page->index < end_index)
2622                 goto out;
2623
2624         /* Is the page fully outside i_size? (truncate in progress) */
2625         offset = i_size & (PAGE_CACHE_SIZE-1);
2626         if (page->index >= end_index+1 || !offset) {
2627                 /*
2628                  * The page may have dirty, unmapped buffers.  For example,
2629                  * they may have been added in ext3_writepage().  Make them
2630                  * freeable here, so the page does not leak.
2631                  */
2632 #if 0
2633                 /* Not really sure about this  - do we need this ? */
2634                 if (page->mapping->a_ops->invalidatepage)
2635                         page->mapping->a_ops->invalidatepage(page, offset);
2636 #endif
2637                 unlock_page(page);
2638                 return 0; /* don't care */
2639         }
2640
2641         /*
2642          * The page straddles i_size.  It must be zeroed out on each and every
2643          * writepage invocation because it may be mmapped.  "A file is mapped
2644          * in multiples of the page size.  For a file that is not a multiple of
2645          * the  page size, the remaining memory is zeroed when mapped, and
2646          * writes to that region are not written out to the file."
2647          */
2648         zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2649 out:
2650         ret = mpage_writepage(page, get_block, wbc);
2651         if (ret == -EAGAIN)
2652                 ret = __block_write_full_page(inode, page, get_block, wbc);
2653         return ret;
2654 }
2655 EXPORT_SYMBOL(nobh_writepage);
2656
2657 int nobh_truncate_page(struct address_space *mapping,
2658                         loff_t from, get_block_t *get_block)
2659 {
2660         pgoff_t index = from >> PAGE_CACHE_SHIFT;
2661         unsigned offset = from & (PAGE_CACHE_SIZE-1);
2662         unsigned blocksize;
2663         sector_t iblock;
2664         unsigned length, pos;
2665         struct inode *inode = mapping->host;
2666         struct page *page;
2667         struct buffer_head map_bh;
2668         int err;
2669
2670         blocksize = 1 << inode->i_blkbits;
2671         length = offset & (blocksize - 1);
2672
2673         /* Block boundary? Nothing to do */
2674         if (!length)
2675                 return 0;
2676
2677         length = blocksize - length;
2678         iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2679
2680         page = grab_cache_page(mapping, index);
2681         err = -ENOMEM;
2682         if (!page)
2683                 goto out;
2684
2685         if (page_has_buffers(page)) {
2686 has_buffers:
2687                 unlock_page(page);
2688                 page_cache_release(page);
2689                 return block_truncate_page(mapping, from, get_block);
2690         }
2691
2692         /* Find the buffer that contains "offset" */
2693         pos = blocksize;
2694         while (offset >= pos) {
2695                 iblock++;
2696                 pos += blocksize;
2697         }
2698
2699         err = get_block(inode, iblock, &map_bh, 0);
2700         if (err)
2701                 goto unlock;
2702         /* unmapped? It's a hole - nothing to do */
2703         if (!buffer_mapped(&map_bh))
2704                 goto unlock;
2705
2706         /* Ok, it's mapped. Make sure it's up-to-date */
2707         if (!PageUptodate(page)) {
2708                 err = mapping->a_ops->readpage(NULL, page);
2709                 if (err) {
2710                         page_cache_release(page);
2711                         goto out;
2712                 }
2713                 lock_page(page);
2714                 if (!PageUptodate(page)) {
2715                         err = -EIO;
2716                         goto unlock;
2717                 }
2718                 if (page_has_buffers(page))
2719                         goto has_buffers;
2720         }
2721         zero_user(page, offset, length);
2722         set_page_dirty(page);
2723         err = 0;
2724
2725 unlock:
2726         unlock_page(page);
2727         page_cache_release(page);
2728 out:
2729         return err;
2730 }
2731 EXPORT_SYMBOL(nobh_truncate_page);
2732
2733 int block_truncate_page(struct address_space *mapping,
2734                         loff_t from, get_block_t *get_block)
2735 {
2736         pgoff_t index = from >> PAGE_CACHE_SHIFT;
2737         unsigned offset = from & (PAGE_CACHE_SIZE-1);
2738         unsigned blocksize;
2739         sector_t iblock;
2740         unsigned length, pos;
2741         struct inode *inode = mapping->host;
2742         struct page *page;
2743         struct buffer_head *bh;
2744         int err;
2745
2746         blocksize = 1 << inode->i_blkbits;
2747         length = offset & (blocksize - 1);
2748
2749         /* Block boundary? Nothing to do */
2750         if (!length)
2751                 return 0;
2752
2753         length = blocksize - length;
2754         iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2755         
2756         page = grab_cache_page(mapping, index);
2757         err = -ENOMEM;
2758         if (!page)
2759                 goto out;
2760
2761         if (!page_has_buffers(page))
2762                 create_empty_buffers(page, blocksize, 0);
2763
2764         /* Find the buffer that contains "offset" */
2765         bh = page_buffers(page);
2766         pos = blocksize;
2767         while (offset >= pos) {
2768                 bh = bh->b_this_page;
2769                 iblock++;
2770                 pos += blocksize;
2771         }
2772
2773         err = 0;
2774         if (!buffer_mapped(bh)) {
2775                 WARN_ON(bh->b_size != blocksize);
2776                 err = get_block(inode, iblock, bh, 0);
2777                 if (err)
2778                         goto unlock;
2779                 /* unmapped? It's a hole - nothing to do */
2780                 if (!buffer_mapped(bh))
2781                         goto unlock;
2782         }
2783
2784         /* Ok, it's mapped. Make sure it's up-to-date */
2785         if (PageUptodate(page))
2786                 set_buffer_uptodate(bh);
2787
2788         if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2789                 err = -EIO;
2790                 ll_rw_block(READ, 1, &bh);
2791                 wait_on_buffer(bh);
2792                 /* Uhhuh. Read error. Complain and punt. */
2793                 if (!buffer_uptodate(bh))
2794                         goto unlock;
2795         }
2796
2797         zero_user(page, offset, length);
2798         mark_buffer_dirty(bh);
2799         err = 0;
2800
2801 unlock:
2802         unlock_page(page);
2803         page_cache_release(page);
2804 out:
2805         return err;
2806 }
2807
2808 /*
2809  * The generic ->writepage function for buffer-backed address_spaces
2810  */
2811 int block_write_full_page(struct page *page, get_block_t *get_block,
2812                         struct writeback_control *wbc)
2813 {
2814         struct inode * const inode = page->mapping->host;
2815         loff_t i_size = i_size_read(inode);
2816         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2817         unsigned offset;
2818
2819         /* Is the page fully inside i_size? */
2820         if (page->index < end_index)
2821                 return __block_write_full_page(inode, page, get_block, wbc);
2822
2823         /* Is the page fully outside i_size? (truncate in progress) */
2824         offset = i_size & (PAGE_CACHE_SIZE-1);
2825         if (page->index >= end_index+1 || !offset) {
2826                 /*
2827                  * The page may have dirty, unmapped buffers.  For example,
2828                  * they may have been added in ext3_writepage().  Make them
2829                  * freeable here, so the page does not leak.
2830                  */
2831                 do_invalidatepage(page, 0);
2832                 unlock_page(page);
2833                 return 0; /* don't care */
2834         }
2835
2836         /*
2837          * The page straddles i_size.  It must be zeroed out on each and every
2838          * writepage invokation because it may be mmapped.  "A file is mapped
2839          * in multiples of the page size.  For a file that is not a multiple of
2840          * the  page size, the remaining memory is zeroed when mapped, and
2841          * writes to that region are not written out to the file."
2842          */
2843         zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2844         return __block_write_full_page(inode, page, get_block, wbc);
2845 }
2846
2847 sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2848                             get_block_t *get_block)
2849 {
2850         struct buffer_head tmp;
2851         struct inode *inode = mapping->host;
2852         tmp.b_state = 0;
2853         tmp.b_blocknr = 0;
2854         tmp.b_size = 1 << inode->i_blkbits;
2855         get_block(inode, block, &tmp, 0);
2856         return tmp.b_blocknr;
2857 }
2858
2859 static void end_bio_bh_io_sync(struct bio *bio, int err)
2860 {
2861         struct buffer_head *bh = bio->bi_private;
2862
2863         if (err == -EOPNOTSUPP) {
2864                 set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
2865                 set_bit(BH_Eopnotsupp, &bh->b_state);
2866         }
2867
2868         if (unlikely (test_bit(BIO_QUIET,&bio->bi_flags)))
2869                 set_bit(BH_Quiet, &bh->b_state);
2870
2871         bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
2872         bio_put(bio);
2873 }
2874
2875 int submit_bh(int rw, struct buffer_head * bh)
2876 {
2877         struct bio *bio;
2878         int ret = 0;
2879
2880         BUG_ON(!buffer_locked(bh));
2881         BUG_ON(!buffer_mapped(bh));
2882         BUG_ON(!bh->b_end_io);
2883
2884         /*
2885          * Mask in barrier bit for a write (could be either a WRITE or a
2886          * WRITE_SYNC
2887          */
2888         if (buffer_ordered(bh) && (rw & WRITE))
2889                 rw |= WRITE_BARRIER;
2890
2891         /*
2892          * Only clear out a write error when rewriting
2893          */
2894         if (test_set_buffer_req(bh) && (rw & WRITE))
2895                 clear_buffer_write_io_error(bh);
2896
2897         /*
2898          * from here on down, it's all bio -- do the initial mapping,
2899          * submit_bio -> generic_make_request may further map this bio around
2900          */
2901         bio = bio_alloc(GFP_NOIO, 1);
2902
2903         bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
2904         bio->bi_bdev = bh->b_bdev;
2905         bio->bi_io_vec[0].bv_page = bh->b_page;
2906         bio->bi_io_vec[0].bv_len = bh->b_size;
2907         bio->bi_io_vec[0].bv_offset = bh_offset(bh);
2908
2909         bio->bi_vcnt = 1;
2910         bio->bi_idx = 0;
2911         bio->bi_size = bh->b_size;
2912
2913         bio->bi_end_io = end_bio_bh_io_sync;
2914         bio->bi_private = bh;
2915
2916         bio_get(bio);
2917         submit_bio(rw, bio);
2918
2919         if (bio_flagged(bio, BIO_EOPNOTSUPP))
2920                 ret = -EOPNOTSUPP;
2921
2922         bio_put(bio);
2923         return ret;
2924 }
2925
2926 /**
2927  * ll_rw_block: low-level access to block devices (DEPRECATED)
2928  * @rw: whether to %READ or %WRITE or %SWRITE or maybe %READA (readahead)
2929  * @nr: number of &struct buffer_heads in the array
2930  * @bhs: array of pointers to &struct buffer_head
2931  *
2932  * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
2933  * requests an I/O operation on them, either a %READ or a %WRITE.  The third
2934  * %SWRITE is like %WRITE only we make sure that the *current* data in buffers
2935  * are sent to disk. The fourth %READA option is described in the documentation
2936  * for generic_make_request() which ll_rw_block() calls.
2937  *
2938  * This function drops any buffer that it cannot get a lock on (with the
2939  * BH_Lock state bit) unless SWRITE is required, any buffer that appears to be
2940  * clean when doing a write request, and any buffer that appears to be
2941  * up-to-date when doing read request.  Further it marks as clean buffers that
2942  * are processed for writing (the buffer cache won't assume that they are
2943  * actually clean until the buffer gets unlocked).
2944  *
2945  * ll_rw_block sets b_end_io to simple completion handler that marks
2946  * the buffer up-to-date (if approriate), unlocks the buffer and wakes
2947  * any waiters. 
2948  *
2949  * All of the buffers must be for the same device, and must also be a
2950  * multiple of the current approved size for the device.
2951  */
2952 void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
2953 {
2954         int i;
2955
2956         for (i = 0; i < nr; i++) {
2957                 struct buffer_head *bh = bhs[i];
2958
2959                 if (rw == SWRITE || rw == SWRITE_SYNC)
2960                         lock_buffer(bh);
2961                 else if (!trylock_buffer(bh))
2962                         continue;
2963
2964                 if (rw == WRITE || rw == SWRITE || rw == SWRITE_SYNC) {
2965                         if (test_clear_buffer_dirty(bh)) {
2966                                 bh->b_end_io = end_buffer_write_sync;
2967                                 get_bh(bh);
2968                                 if (rw == SWRITE_SYNC)
2969                                         submit_bh(WRITE_SYNC, bh);
2970                                 else
2971                                         submit_bh(WRITE, bh);
2972                                 continue;
2973                         }
2974                 } else {
2975                         if (!buffer_uptodate(bh)) {
2976                                 bh->b_end_io = end_buffer_read_sync;
2977                                 get_bh(bh);
2978                                 submit_bh(rw, bh);
2979                                 continue;
2980                         }
2981                 }
2982                 unlock_buffer(bh);
2983         }
2984 }
2985
2986 /*
2987  * For a data-integrity writeout, we need to wait upon any in-progress I/O
2988  * and then start new I/O and then wait upon it.  The caller must have a ref on
2989  * the buffer_head.
2990  */
2991 int sync_dirty_buffer(struct buffer_head *bh)
2992 {
2993         int ret = 0;
2994
2995         WARN_ON(atomic_read(&bh->b_count) < 1);
2996         lock_buffer(bh);
2997         if (test_clear_buffer_dirty(bh)) {
2998                 get_bh(bh);
2999                 bh->b_end_io = end_buffer_write_sync;
3000                 ret = submit_bh(WRITE, bh);
3001                 wait_on_buffer(bh);
3002                 if (buffer_eopnotsupp(bh)) {
3003                         clear_buffer_eopnotsupp(bh);
3004                         ret = -EOPNOTSUPP;
3005                 }
3006                 if (!ret && !buffer_uptodate(bh))
3007                         ret = -EIO;
3008         } else {
3009                 unlock_buffer(bh);
3010         }
3011         return ret;
3012 }
3013
3014 /*
3015  * try_to_free_buffers() checks if all the buffers on this particular page
3016  * are unused, and releases them if so.
3017  *
3018  * Exclusion against try_to_free_buffers may be obtained by either
3019  * locking the page or by holding its mapping's private_lock.
3020  *
3021  * If the page is dirty but all the buffers are clean then we need to
3022  * be sure to mark the page clean as well.  This is because the page
3023  * may be against a block device, and a later reattachment of buffers
3024  * to a dirty page will set *all* buffers dirty.  Which would corrupt
3025  * filesystem data on the same device.
3026  *
3027  * The same applies to regular filesystem pages: if all the buffers are
3028  * clean then we set the page clean and proceed.  To do that, we require
3029  * total exclusion from __set_page_dirty_buffers().  That is obtained with
3030  * private_lock.
3031  *
3032  * try_to_free_buffers() is non-blocking.
3033  */
3034 static inline int buffer_busy(struct buffer_head *bh)
3035 {
3036         return atomic_read(&bh->b_count) |
3037                 (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3038 }
3039
3040 static int
3041 drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
3042 {
3043         struct buffer_head *head = page_buffers(page);
3044         struct buffer_head *bh;
3045
3046         bh = head;
3047         do {
3048                 if (buffer_write_io_error(bh) && page->mapping)
3049                         set_bit(AS_EIO, &page->mapping->flags);
3050                 if (buffer_busy(bh))
3051                         goto failed;
3052                 bh = bh->b_this_page;
3053         } while (bh != head);
3054
3055         do {
3056                 struct buffer_head *next = bh->b_this_page;
3057
3058                 if (bh->b_assoc_map)
3059                         __remove_assoc_queue(bh);
3060                 bh = next;
3061         } while (bh != head);
3062         *buffers_to_free = head;
3063         __clear_page_buffers(page);
3064         return 1;
3065 failed:
3066         return 0;
3067 }
3068
3069 int try_to_free_buffers(struct page *page)
3070 {
3071         struct address_space * const mapping = page->mapping;
3072         struct buffer_head *buffers_to_free = NULL;
3073         int ret = 0;
3074
3075         BUG_ON(!PageLocked(page));
3076         if (PageWriteback(page))
3077                 return 0;
3078
3079         if (mapping == NULL) {          /* can this still happen? */
3080                 ret = drop_buffers(page, &buffers_to_free);
3081                 goto out;
3082         }
3083
3084         spin_lock(&mapping->private_lock);
3085         ret = drop_buffers(page, &buffers_to_free);
3086
3087         /*
3088          * If the filesystem writes its buffers by hand (eg ext3)
3089          * then we can have clean buffers against a dirty page.  We
3090          * clean the page here; otherwise the VM will never notice
3091          * that the filesystem did any IO at all.
3092          *
3093          * Also, during truncate, discard_buffer will have marked all
3094          * the page's buffers clean.  We discover that here and clean
3095          * the page also.
3096          *
3097          * private_lock must be held over this entire operation in order
3098          * to synchronise against __set_page_dirty_buffers and prevent the
3099          * dirty bit from being lost.
3100          */
3101         if (ret)
3102                 cancel_dirty_page(page, PAGE_CACHE_SIZE);
3103         spin_unlock(&mapping->private_lock);
3104 out:
3105         if (buffers_to_free) {
3106                 struct buffer_head *bh = buffers_to_free;
3107
3108                 do {
3109                         struct buffer_head *next = bh->b_this_page;
3110                         free_buffer_head(bh);
3111                         bh = next;
3112                 } while (bh != buffers_to_free);
3113         }
3114         return ret;
3115 }
3116 EXPORT_SYMBOL(try_to_free_buffers);
3117
3118 void block_sync_page(struct page *page)
3119 {
3120         struct address_space *mapping;
3121
3122         smp_mb();
3123         mapping = page_mapping(page);
3124         if (mapping)
3125                 blk_run_backing_dev(mapping->backing_dev_info, page);
3126 }
3127
3128 /*
3129  * There are no bdflush tunables left.  But distributions are
3130  * still running obsolete flush daemons, so we terminate them here.
3131  *
3132  * Use of bdflush() is deprecated and will be removed in a future kernel.
3133  * The `pdflush' kernel threads fully replace bdflush daemons and this call.
3134  */
3135 SYSCALL_DEFINE2(bdflush, int, func, long, data)
3136 {
3137         static int msg_count;
3138
3139         if (!capable(CAP_SYS_ADMIN))
3140                 return -EPERM;
3141
3142         if (msg_count < 5) {
3143                 msg_count++;
3144                 printk(KERN_INFO
3145                         "warning: process `%s' used the obsolete bdflush"
3146                         " system call\n", current->comm);
3147                 printk(KERN_INFO "Fix your initscripts?\n");
3148         }
3149
3150         if (func == 1)
3151                 do_exit(0);
3152         return 0;
3153 }
3154
3155 /*
3156  * Buffer-head allocation
3157  */
3158 static struct kmem_cache *bh_cachep;
3159
3160 /*
3161  * Once the number of bh's in the machine exceeds this level, we start
3162  * stripping them in writeback.
3163  */
3164 static int max_buffer_heads;
3165
3166 int buffer_heads_over_limit;
3167
3168 struct bh_accounting {
3169         int nr;                 /* Number of live bh's */
3170         int ratelimit;          /* Limit cacheline bouncing */
3171 };
3172
3173 static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3174
3175 static void recalc_bh_state(void)
3176 {
3177         int i;
3178         int tot = 0;
3179
3180         if (__get_cpu_var(bh_accounting).ratelimit++ < 4096)
3181                 return;
3182         __get_cpu_var(bh_accounting).ratelimit = 0;
3183         for_each_online_cpu(i)
3184                 tot += per_cpu(bh_accounting, i).nr;
3185         buffer_heads_over_limit = (tot > max_buffer_heads);
3186 }
3187         
3188 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3189 {
3190         struct buffer_head *ret = kmem_cache_alloc(bh_cachep, gfp_flags);
3191         if (ret) {
3192                 INIT_LIST_HEAD(&ret->b_assoc_buffers);
3193                 get_cpu_var(bh_accounting).nr++;
3194                 recalc_bh_state();
3195                 put_cpu_var(bh_accounting);
3196         }
3197         return ret;
3198 }
3199 EXPORT_SYMBOL(alloc_buffer_head);
3200
3201 void free_buffer_head(struct buffer_head *bh)
3202 {
3203         BUG_ON(!list_empty(&bh->b_assoc_buffers));
3204         kmem_cache_free(bh_cachep, bh);
3205         get_cpu_var(bh_accounting).nr--;
3206         recalc_bh_state();
3207         put_cpu_var(bh_accounting);
3208 }
3209 EXPORT_SYMBOL(free_buffer_head);
3210
3211 static void buffer_exit_cpu(int cpu)
3212 {
3213         int i;
3214         struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3215
3216         for (i = 0; i < BH_LRU_SIZE; i++) {
3217                 brelse(b->bhs[i]);
3218                 b->bhs[i] = NULL;
3219         }
3220         get_cpu_var(bh_accounting).nr += per_cpu(bh_accounting, cpu).nr;
3221         per_cpu(bh_accounting, cpu).nr = 0;
3222         put_cpu_var(bh_accounting);
3223 }
3224
3225 static int buffer_cpu_notify(struct notifier_block *self,
3226                               unsigned long action, void *hcpu)
3227 {
3228         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN)
3229                 buffer_exit_cpu((unsigned long)hcpu);
3230         return NOTIFY_OK;
3231 }
3232
3233 /**
3234  * bh_uptodate_or_lock - Test whether the buffer is uptodate
3235  * @bh: struct buffer_head
3236  *
3237  * Return true if the buffer is up-to-date and false,
3238  * with the buffer locked, if not.
3239  */
3240 int bh_uptodate_or_lock(struct buffer_head *bh)
3241 {
3242         if (!buffer_uptodate(bh)) {
3243                 lock_buffer(bh);
3244                 if (!buffer_uptodate(bh))
3245                         return 0;
3246                 unlock_buffer(bh);
3247         }
3248         return 1;
3249 }
3250 EXPORT_SYMBOL(bh_uptodate_or_lock);
3251
3252 /**
3253  * bh_submit_read - Submit a locked buffer for reading
3254  * @bh: struct buffer_head
3255  *
3256  * Returns zero on success and -EIO on error.
3257  */
3258 int bh_submit_read(struct buffer_head *bh)
3259 {
3260         BUG_ON(!buffer_locked(bh));
3261
3262         if (buffer_uptodate(bh)) {
3263                 unlock_buffer(bh);
3264                 return 0;
3265         }
3266
3267         get_bh(bh);
3268         bh->b_end_io = end_buffer_read_sync;
3269         submit_bh(READ, bh);
3270         wait_on_buffer(bh);
3271         if (buffer_uptodate(bh))
3272                 return 0;
3273         return -EIO;
3274 }
3275 EXPORT_SYMBOL(bh_submit_read);
3276
3277 static void
3278 init_buffer_head(void *data)
3279 {
3280         struct buffer_head *bh = data;
3281
3282         memset(bh, 0, sizeof(*bh));
3283         INIT_LIST_HEAD(&bh->b_assoc_buffers);
3284 }
3285
3286 void __init buffer_init(void)
3287 {
3288         int nrpages;
3289
3290         bh_cachep = kmem_cache_create("buffer_head",
3291                         sizeof(struct buffer_head), 0,
3292                                 (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3293                                 SLAB_MEM_SPREAD),
3294                                 init_buffer_head);
3295
3296         /*
3297          * Limit the bh occupancy to 10% of ZONE_NORMAL
3298          */
3299         nrpages = (nr_free_buffer_pages() * 10) / 100;
3300         max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3301         hotcpu_notifier(buffer_cpu_notify, 0);
3302 }
3303
3304 EXPORT_SYMBOL(__bforget);
3305 EXPORT_SYMBOL(__brelse);
3306 EXPORT_SYMBOL(__wait_on_buffer);
3307 EXPORT_SYMBOL(block_commit_write);
3308 EXPORT_SYMBOL(block_prepare_write);
3309 EXPORT_SYMBOL(block_page_mkwrite);
3310 EXPORT_SYMBOL(block_read_full_page);
3311 EXPORT_SYMBOL(block_sync_page);
3312 EXPORT_SYMBOL(block_truncate_page);
3313 EXPORT_SYMBOL(block_write_full_page);
3314 EXPORT_SYMBOL(cont_write_begin);
3315 EXPORT_SYMBOL(end_buffer_read_sync);
3316 EXPORT_SYMBOL(end_buffer_write_sync);
3317 EXPORT_SYMBOL(file_fsync);
3318 EXPORT_SYMBOL(generic_block_bmap);
3319 EXPORT_SYMBOL(generic_cont_expand_simple);
3320 EXPORT_SYMBOL(init_buffer);
3321 EXPORT_SYMBOL(invalidate_bdev);
3322 EXPORT_SYMBOL(ll_rw_block);
3323 EXPORT_SYMBOL(mark_buffer_dirty);
3324 EXPORT_SYMBOL(submit_bh);
3325 EXPORT_SYMBOL(sync_dirty_buffer);
3326 EXPORT_SYMBOL(unlock_buffer);